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. 2004 Aug;137(2):437–443. doi: 10.1111/j.1365-2249.2004.02536.x

The number of CD8+ T cells and NKT cells increases in the aqueous humor of patients with Behçet's uveitis

H G Yu *, D S Lee †, J M Seo *, J K Ahn *, Y S Yu *, W J Lee †, H Chung *
PMCID: PMC1809124  PMID: 15270864

Abstract

To determine whether there are differences in the immunopathogenesis of different endogenous uveitis syndromes, the phenotypic characteristics of immune cells were analysed among patients with endogenous uveitis. The aetiology of the uveitis included idiopathic recurrent acute anterior uveitis (18 patients), idiopathic intermediate uveitis (13 patients), Behçet's uveitis (17 patients), Vogt–Koyanagi–Harada syndrome (7 patients), and so on. Flow cytometric analysis was performed using immune cells of the aqueous humor and the peripheral blood during the active phase of intraocular inflammation, and monoclonal antibodies to CD3, CD4, CD8, CD14, CD19, CD56, TCR γδ, pan TCR αβ and Vα24. CD8+ T cells were predominant in the aqueous humor of the patients with Behçet's uveitis, whereas CD4+ T cells were mainly found in the aqueous humor of patients other than those with Behçet's uveitis. The number of NKT (CD3+CD56+) cells was significantly higher both in the aqueous humor and the peripheral blood of the patients with Behçet's uveitis compared with the other groups (P < 0·05). CD8+CD56+ cells were the predominant subtype of the increased NKT cells in patients with Behçet's uveitis. In addition, intraocular infiltration of CD14+ cells significantly differed among the uveitis patients (P < 0·05). These results suggest that the immunopathogenesis of endogenous uveitis can vary between syndromes, and that CD8+CD56+ NKT cells may play an important role in the immunopathogenesis of Behçet's uveitis.

Keywords: uveitis, Behçet's disease, aqueous humor, NKT cell

INTRODUCTION

Endogenous uveitis is an intraocular inflammatory disease, which can lead to blindness in many cases. In Asians, uveitis often appears as a manifestation of systemic diseases such as Behçet's disease or Vogt–Koyanagi–Harada (VKH) syndrome, whereas the majority of uveitis is still of an idiopathic origin (i.e. there are no systemic features on questioning or on investigation). Although endogenous uveitis covers a range of different clinical entities, all forms are believed to be similar immunohistologically, which are characterized by the infiltration mainly of T cells [1,2]. Therefore, endogenous uveitis in humans is believed to be a T cell-mediated autoimmune disease, although the immunopathogenic mechanisms are unclear [3,4].

However, previous studies on the phenotypes of the infiltrating inflammatory cells in uveitis patients showed some different results, implying that different immunopathogenic mechanisms may be involved with the development of the various subtypes of uveitis [5–8]. In addition, it is unclear whether the immune processes in the development of intraocular inflammation are identical to those of other systemic manifestations in uveitis associated with a systemic disease, because the ocular inflammatory activity does not always occur in parallel with the activity of the associated systemic inflammation. Therefore, it is possible that different immunopathogenic mechanisms and immune cells may be involved in the development of different endogenous uveitis syndromes.

Natural killer T (NKT) cells are heterogeneous T cell populations that are characterized by the coexpression of TCRs and various NK receptors, including CD16, CD56, CD161, CD94, CD158a and CD158b [9]. NKT cells have been considered to regulate autoimmunity and adaptive immune responses [9–11], even though the pleiotropic nature of NKT cells creates some controversy regarding the functional role at different inflammatory sites [12–15]. Disturbances in the numbers and functions of the NKT cells have been implicated in several organ-specific animal models of autoimmunity as well as in humans [16–18]. It was reported that the proportion of CD56+ T cells in the peripheral blood of patients with Behçet's uveitis, which is a prototype of chronic and recurrent uveitis with multisystemic manifestations, was higher than those of other uveitis patients and healthy controls [19]. However, the proportion of NKT cells among the infiltrating intraocular cells in the uveitis patients has not yet been studied.

Therefore, in this study we asked whether there are phenotypic differences in the intraocular immune cell types, including the NKT cells, in the patients with endogenous uveitis according to the specific diagnosis. Moreover, the subtypes of CD56+ T cells, including γδ T cells, Vα24+ T cells and CD8+CD56+ T cells, were analysed in the aqueous humor (intraocular fluid from the anterior chamber) and peripheral blood.

MATERIALS AND METHODS

Patients

Sixty-three patients (39 men and 24 women, age range 13–66 years) with uveitis of different aetiologies were recruited from the uveitis clinic at Seoul National University Hospital. All patients had not used corticosteroids (topical, oral and intravenous) or immunosuppressive agents such as cyclosporin A within recent one month, and had an active intraocular inflammation (anterior chamber cells ≥2+). The aqueous humor and the blood samples were obtained before the start of any topical or systemic treatment. Ethics committee approval for this study was received, and informed consent was obtained from all participants. The study adhered to the principles of the Declaration of Helsinki.

The majority of patients could be diagnosed with one of four conditions: recurrent acute anterior uveitis, idiopathic intermediate uveitis, Behçet's uveitis or Vogt–Koyanagi–Harada syndrome. Recurrent acute anterior uveitis and intermediate uveitis were diagnosed only after a detailed history, and the laboratory tests were all negative except HLA B27 which was positive in 8 of 19 anterior uveitis patients. Seventeen patients with Behçet's uveitis showed the ‘complete type’ of Behçet's disease according to the criteria of the Japanese Behçet's disease research committee, and also satisfied the criteria suggested by the International Study Group for Behçet's Disease [20,21]. The remaining patients were diagnosed as having sarcoidosis (n = 2), ankylosing spondylitis (n = 2), juvenile rheumatoid arthritis (n = 2), psoriatic arthritis (n = 1) and systemic lupus erythematosis (n = 1) (Table 1).

Table 1.

Patient profiles in this study

Diagnosis Sex (M : F) Age (years) Disease duration (months)
Recurrent acute anterior uveitis  (n = 18) 9 : 9 46·3 ± 14·6 26·3 ± 18·7
Intermediate uveitis (n = 13) 8 : 5 39·4 ± 15·7 30·9 ± 22·9
Behçet disease (n = 17) 15 : 2 36·8 ± 8·7 40·4 ± 28·6
Vogt–Koyanagi–Harada syndrome  (n = 7) 3 : 4 46·6 ± 12·2 33·6 ± 23·6
Others (n = 8) 4 : 4 35·7 ± 18·3 31·5 ± 19·7
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Aqueous humor sampling procedure

Anterior chamber paracentesis was carried out using a 30-gauge needle, on a 1 ml insulin syringe, using the temporal limbal approach and a rolling technique. 100–200 µl of aqueous humor was aspirated and immediately placed into a microcentrifuge tube precoated with EDTA used to prevent cell clumping. Immunofluorescence staining was immediately performed.

Immunofluorescence and flow cytometric analysis

Heparinized venous blood was obtained from the uveitis patients and healthy controls. The peripheral blood mononuclear cells (PBMCs) were isolated by centrifugation at 400 g on a Ficoll-Hypaque (Pharmacia Biotech, Uppsala, Sweden) gradient. The PBMCs were recovered at the buffy coat layer and washed twice to remove the red blood cells. The cells were washed twice in phosphate-buffered saline before being resuspended in a FACS buffer (BD Biosciences, Franklin Lakes, NJ, USA). Three-colour staining of the anterior chamber cells and the PBMCs was performed using monoclonal antibodies (mAbs), in two combinations: tube A contained mAbs to CD4 (helper T cell)/CD8 (cytotoxic T cell)/CD19 (B cell), and tube B contained mAbs to CD3 (Pan T cell)/CD56 (Natural killer cell)/CD14 (monocyte; all were products of BD Biosciences).

The isotype-matched control mAbs were used as the control using PBMCs. 100 µl aliquots of the mononuclear cells from the aqueous humor or blood were added to the polypropylene round-bottom test tube, and the directly conjugated mAbs (conjugated fluorescein isothiocyanate (FITC), phycoerythrin (PE), Cy-Chrome (Cy) or Peridinin Chlorophyll-a Protein (PerCP)) were added at predetermined optimal dilution. The isotype-matched control was prepared from the PBMCs. After a 30-minute incubation, aliquots were washed twice in FACS buffer (phosphate-buffered saline/0·2% bovine serum albumin). The acquisition was performed on a BD FACSCalibur™ System or BD FACScan™ Cytometer and analysed using the CellQuest™ software program (BD Biosciences). A gate for the live lymphocyte population was defined by the forward and side scatter characteristics, and the data was displayed on a log scale of increasing florescence intensity.

In addition, the subtype analysis of CD3+CD56+ cells was done in the aqueous humor and the peripheral blood of patients with idiopathic anterior uveitis (n = 11) and Behçet's uveitis (n = 11) at the time of active inflammation. The subtype analysis was also done to 15 healthy controls for the comparison. CD3+CD56+ T cells belong to a highly heterogeneous subset that includes chronically stimulated conventional CD8+ T cells, γδ T cells and so called CD1d-restricted NKT cells, the hallmark of which is the recurrent expression of Vα24Vb11 T cell receptors [22]. For the further detailed phenotypic analysis of CD3+CD56+ T cells, three or four colour staining, using CD3, CD56 and additional markers such as pan TCR γδ mAb, pan TCR β mAb, CD4 and CD8 coreceptors and Vα24 Vβ11 (all were products of BD Biosciences) were done. Furthermore, activation markers (CD69 and CD25) of CD4+ T cells in the aqueous humor and the peripheral blood of uveitis patients were analysed.

Statistics

The differences in the phenotypic characteristics of the mononuclear cell populations among the patients with recurrent acute anterior uveitis, idiopathic intermediate uveitis, Behçet's uveitis, Vogt–Koyanagi–Harada syndrome, were statistically compared using Anova test. For significant Anova values, the groups were compared by a Tukey's post hoc test for the multiple comparisons with an unequal cell size. A P-value < 0·05 was considered significant. In addition, the Wilcoxon matched-pair signed-rank test was used to demonstrate the differences between the values obtained from the aqueous humor and those from the blood samples of the same patient.

RESULTS

Cell types in aqueous humor and peripheral blood

The aqueous humor and the peripheral blood from the patients were analysed for the percentages of B cells (CD19), CD4 and CD8+ T cell subsets among the lymphocytes (R1). In addition, the percentage of monocytes (CD14) was calculated from the total gated population of the lymphocyte and monocyte region (R2; Fig. 1a,d).

Fig. 1.

Fig. 1

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Representative dot-plot diagrams of the aqueous humor cells from patients with anterior uveitis (a,b,c) and patients with Behçet's uveitis (d,e,f). The region where lymphocytes (R1) or monocytes (R2) were accumulated was gated according to forward scatter and side scatter. The percentages of CD4+, CD8+, CD3+, CD3-CD56+ and CD3+CD56+ T cell subsets among the lymphocytes (R1) were written in the diagrams (b,c,e,f).

The phenotypes of the immune cells showed significant differences between the aqueous humor and the peripheral blood and varied according to the specific diagnosis (Table 2). In general, the percentage of CD4+ cells in the aqueous humor of uveitis patients was elevated resulting in a higher CD4+/CD8+ T cell ratio compared to the peripheral blood. The patients with Behçet's uveitis, however, showed a higher CD8+ cell percentage and a reversed CD4+/CD8+ T cell ratio in the aqueous humor. The calculated percentage of CD4+ cells by subtracting that of CD8+ cells from that of CD3+ cells was similar with the actual percentage of CD4+ cells, which indicates that CD4 down regulation in the experimental system does not affect our results. Representative flow cytometric analyses show CD4+ and CD8+ cells in the aqueous humor of the patients with idiopathic anterior uveitis (Fig. 1b) versus Behçet's uveitis (Fig. 1e). The percentage of CD69+ or CD25+ cells of CD4+ T cells was higher in the aqueous humor of patients with idiopathic anterior uveitis than Behcet's uveitis (57·1 ± 18·2% in idiopathic anterior uveitis versus 12·6 ± 6·4% in Behcet's uveitis), in contrast to the peripheral blood, where they were similarly expressed in low levels independently of uveitis diagnosis (2·4 ± 1·0% in idiopathic anterior uveitis versus 1·8 ± 1·1% in Behcet's uveitis).

Table 2.

Percentages and ratio of lymphocyte subsets in the peripheral blood and aqueous humor of patients with uveitis according to the specific diagnoses

Recurrent acute anterior uveitis (n = 18) Intermediate uveitis (n = 13) Behçet’s uveitis (n = 17) Vogt–Koyanagi– Harada syndrome (n = 7) Others (n = 8)
Blood
 CD3+ 81·85 ± 6·45 82·87 ± 7·59 78·75 ± 5·71 82·11 ± 7·14 82·70 ± 11·04
 CD4+ 46·20 ± 6·48 49·78 ± 9·64 40·47 ± 10·81 47·74 ± 10·85 38·47 ± 5·75
 CD8+ 28·34 ± 6·16 31·34 ± 9·98 32·89 ± 7·75 26·28 ± 4·54 27·70 ± 5·40
 CD4+/CD8+ 1·61 ± 0·51 1·89 ± 0·82 1·36 ± 0·67 1·82 ± 0·56 1·36 ± 0·33
 CD19+ 11·03 ± 5·00 8·12 ± 5·53 5·83 ± 5·23 12·43 ± 5·75 8·90 ± 3·72
 CD14+ 8·35 ± 3·38 11·80 ± 3·68 13·05 ± 5·02 15·55 ± 7·88 11·32 ± 3·30
Aqueous humor
 CD3+ 89·8 ± 5·94 91·02 ± 4·37 89·11 ± 6·89 90·11 ± 7·15 89·41 ± 9·41
 CD4+ 53·38 ± 8·28 58·18 ± 16·33 29·65 ± 11·10* 47·33 ± 13·65 48·76 ± 25·66
 CD8+ 30·47 ± 14·37 31·20 ± 13·37 55·00 ± 12·69* 34·53 ± 7·97 34·09 ± 17·03
 CD4+/CD8+ 2·42 ± 0·84 2·37 ± 0·67 0·60 ± 0·35* 1·58 ± 0·74 2·61 ± 0·70
 CD19+ 1·93 ± 0·62 3·30 ± 2·01 1·78 ± 1·07 5·37 ± 2·74 5·65 ± 5·76
 CD14+ 15·11 ± 8·97 25·95 ± 17·47 36·50 ± 11·17* 28·43 ± 14·58 18·29 ± 13·88
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*

denotes statistically significant difference of the value when compared with that of the patients with idiopathic anterior uveitis (P < 0·05).

The proportions of CD3+CD56+ and CD3-CD56+ cells in the aqueous humor and peripheral blood of patients with Behçet's uveitis were higher compared to the other uveitis subtypes (Table 3). Representative flow cytometric analyses show CD3+CD56+ and CD3-CD56+ cells in the aqueous humor of the patients with idiopathic anterior uveitis (Fig. 1c) versus Behçet's uveitis (Fig. 1f). The CD3+CD56+/CD3-CD56+ cellular ratio was significantly different between the aqueous humor and the peripheral blood of patients with Behçet's uveitis because of the more dominance of the NKT cells in the aqueous humor (P < 0·05) (Fig. 2).

Table 3.

Percentages and ratio of NKT (CD3+CD56+) cells and NK (CD3-CD56+) cells in the peripheral blood and aqueous humor of patients with uveitis according to the specific diagnoses

Recurrent acute anterior uveitis (n = 18) Intermediate uveitis (n = 13) Behçet’s uveitis (n = 17) Vogt–Koyanagi– Harada syndrome (n = 7) Others (n = 8)
Blood
 CD3+CD56+ 2·95 ± 1·72 3·40 ± 1·64 11·68 ± 4·18* 3·61 ± 2·01 3·12 ± 2·42
 CD3-CD56+ 7·79 ± 4·59 6·10 ± 3·25 10·26 ± 4·72 6·87 ± 2·72 7·21 ± 4·91
 NKT/NK 0·41 ± 0·33 0·58 ± 0·35 1·21 ± 0·56 0·61 ± 0·29 0·45 ± 0·32
Aqueous humor
 CD3+CD56+ 1·05 ± 0·59 1·52 ± 1·32 13·69 ± 5·39* 2·10 ± 1·77 1·87 ± 1·52
 CD3-CD56+ 2·32 ± 1·28 3·20 ± 2·03 9·82 ± 4·21* 2·71 ± 1·45 2·91 ± 1·98
 NKT/NK 0·61 ± 0·37 0·72 ± 0·47 1·71 ± 0·66* 0·76 ± 0·32 0·69 ± 0·51
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*

denotes statistically significant difference of the value when compared with that of the patients with idiopathic anterior uveitis (P < 0·05).

Fig. 2.

Fig. 2

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Representative dot-plot diagrams of peripheral blood lymphocytes of patients with anterior uveitis (a,b) and patients with Behçet's uveitis (c,d).

In addition, the intraocular infiltration of CD14+ cells was significantly different among the uveitis patients (P < 0·05). The mean percentage of CD14+ cells was lowest in the idiopathic recurrent anterior uveitis patients and highest in the Behçet's uveitis patients. There was a significant decrease in the CD19+ cells in the aqueous humor of patients with endogenous uveitis compared to the peripheral blood (P < 0·05) (Table 2).

Phenotypic analysis of CD3+CD56+ cells in patients with Behcet's uveitis

The subsets of CD3+CD56+ cells in patients with idiopathic anterior uveitis and Behçet's uveitis were analysed in the aqueous humor and the peripheral blood, and we also analysed these cells in healthy controls (Table 4). Representative flow cytometric analyses show CD8+CD56+ and CD56+ γδ T cells in the aqueous humor of the patients with idiopathic anterior uveitis versus Behçet's uveitis (Fig. 3). In the subsets of CD3+CD56+ cells, especially CD8+CD56+ cells and CD56+ γδ T cells, were significantly increased in patients with Behçet's uveitis compared with healthy controls and patients with idiopathic anterior uveitis. In the aqueous humor of patients with idiopathic anterior uveitis, CD3+CD56+ cells were few, so the percentages of the subsets were also minimal and we detected no significant difference, while these cell populations in the peripheral blood were not different from those of healthy controls. On the other hand, in Behçet's uveitis, CD8+CD56+ cells were predominant among the CD3+CD56+ cells in the aqueous humor, followed by CD56+ γδ T cells; CD8+CD56+ cells and CD56+ γδ T cells were similarly predominant among the CD3+CD56+ cells in the peripheral blood. The total number of γδ T cells (with or without CD56 expression) was also significantly increased in the aqueous humor (6·7 ± 1·7%) and the peripheral blood (10·7 ± 5·2%) of the patients with Behçet's uveitis compared to idiopathic anterior uveitis patients (2·9 ± 1·4% in the aqueous humor and 4·9 ± 3·0% in the peripheral blood, respectively; P < 0·05). We observed the similar findings in two active cases among five Behcet's disease without history of uveitis and found that the increased number of CD3+CD56+ T cells was correlated with the inflammatory activity in Behcet's uveitis patients (data not shown). However, Vα24+ T cells among CD3+CD56+ cells were very minimal, and did not show any statistically significant difference among the groups and between the aqueous humor and the peripheral blood.

Table 4.

Percentages of subpopulations of NKT (CD3+CD56+) cells in the peripheral blood and aqueous humor of patients with uveitis according to the specific diagnoses

Lymphocytes Control(n = 15) Peripheral blood Aqueous humor
Recurrent acute anterior uveitis (n = 11) Behçet’s uveitis (n = 11) Recurrent acute anterior uveitis (n = 11) Behçet’s uveitis (n = 11)
CD3+ 56+ cells 4·11 ± 1·57 3·92 ± 2·17 12·03 ± 5·39* 2·82 ± 1·91 12·27 ± 5·92*
CD4+CD56+ cells 0·52 ± 0·28 0·50 ± 0·43 0·51 ± 0·46 0·81 ± 0·51 1·01 ± 0·91
CD8+CD56+ cells 2·01 ± 1·03 1·92 ± 1·12 6·46 ± 3·22* 1·50 ± 1·02 9·92 ± 4·02*
CD56+ αβ TCR 2·29 ± 1·09 2·28 ± 1·01 6·78 ± 3·08* 2·20 ± 1·37 10·91 ± 5·91*
CD56+ γδ TCR 1·84 ± 1·02 1·60 ± 1·40 5·50 ± 3·84* 0·81 ± 0·59 1·77 ± 0·62
CD56+ Vα24+ T cells 0·11 ± 0·05 0·10 ± 0·04 0·13 ± 0·07 0·08 ± 0·05 0·14 ± 0·11
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*

denotes statistically significant difference of the value when compared with that of the controls (P < 0·05).

Fig. 3.

Fig. 3

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Representative dot-plot diagrams of dual staining for CD8/CD56 and CD56/γδ TCR surface markers from patients with anterior uveitis (a,d) and patients with Behçet's uveitis (b,c,e,f). Lymphocytes were obtained from the aqueous humor (a,b,c) and the peripheral blood (d,e, f).

DISCUSSION

This study shows that the immune cell types in the aqueous humor of patients with chronic endogenous uveitis are significantly different among the specific diagnoses of uveitis. In particular, in patients with Behçet's uveitis, the cell types of the intraocular infiltrating cells were significantly different from those in the other endogenous uveitis patients. These results indicate that some different pathogenic mechanism may be involved in Behçet's uveitis compared to the other subtypes of uveitis.

The findings on the distribution of the CD4+ and CD8+ subsets in the inflammatory aqueous humor are somewhat different among the previous reports [23–25]. These inconsistent observations may be attributed to the fact that the aetiologies of the different types of uveitis such as infectious uveitis were included in the previous reports. This study enrolled only patients who had been followed up for at least 6 months and excluded other aetiologies than endogenous uveitis and the patients with systemic steroid or immunosuppressive agents, so our result shows a relatively consistent distribution of lymphocyte subsets percentages according to a subtype of endogenous uveitis. In our patients with idiopathic anterior and intermediate uveitis, CD4+ T cells were more predominant in the aqueous humor than the peripheral blood. These findings are similar with those of previous reports [26,27]. The CD4+ T cells in the aqueous humor of anterior uveitis patients were reported to show significantly increased CD69 and CD25 expression [26]. We also confirmed the higher expression of activation markers (CD69, CD25) of CD4+ T cells in the aqueous humor of our patients with idiopathic anterior uveitis. These results show that CD4+ T cell-mediated immune response plays a key role in the pathogenesis of idiopathic anterior uveitis. However, these activation markers were lower in our patients with Behçet's uveitis, which implies that the role of CD4+ cells is not so important in Behçet's uveitis as anterior uveitis.

In this study, CD3+CD56+ cell population was much higher in the aqueous humor of Behçet's uveitis patients than patients with other endogenous uveitis; it was also higher than that in their peripheral blood. In contrast, CD3+CD56+ cell population in the aqueous humor of other uveitis patients was lower than that in their peripheral blood. These results indicate that CD3+CD56+ cells may play a key role only in the pathogenesis of Behçet's uveitis. Ohkawa et al. [28] suggested that human CD56+ T cells play an important role in the T helper 1 responses. Therefore, activated T cells with NK cell markers (NKT cells) in our Behçet's patients may be harmful to the eye.

Behçet's disease is a unique condition in which there is a dysregulation of the response of the immune system to microorganisms in genetically predisposed individuals even though the aetiology and immunopathogenesis of this disease remains unclear [29]. In addition, Behçet's uveitis is a prototype of chronic and recurrent uveitis resulting in severe tissue damage and permanent visual loss [30]. The fact that NKT cells were increased only in Behçet's uveitis patients may be associated with a unique immunopathogenesis and the more recurrent or chronic nature of Behçet's uveitis compared with other chronic uveitis.

Even though γδ T cells is well known to increase in the peripheral blood of Behçet's patients with mucocutatneous manifestations, the increase of CD8+CD56+ cells in Behçet's patient has not yet been reported [31]. The importance of these cells in the development of ocular inflammation in Behçet's disease is further supported by the fact that CD8+CD56+ cells is more prominent in the aqueous humor rather than in the peripheral blood. Pittet et al. [32] suggested that the CD8+ cytotoxic T lymphocyte (CTL) effector function correlates better with CD56 surface expression. Based on the tight association between cytolytic effector function and CD56 expression, they proposed that CD56 represents a useful marker to identify and monitor effector CD8+ T cells in different clinical situations. These immune cells with cytolytic effector potential may contribute to the more chronic and destructive nature of Behçet's uveitis compared to other endogenous uveitis syndromes that is mediated by CD4+ T cells. Functional study such as cytotoxic functional assay will be necessary in order to determine the exact pathogenic role of CD8+CD56+ cells in the development of Behçet's uveitis.

In this study, γδ T cells with or without CD56 were also increased in Behçet's uveitis patients. γδ T cells are predominantly CD4-CD8- T lymphocytes, appear early in thymic ontogeny, consist 1% to 10% of the peripheral blood T cells, and are dispersed in lymphatic and extralymphatic tissues. γδ T cells work as first-line defending cells of the innate immune response and are thought to influence the nature of the adaptive immune response [33]. Especially, γδ T cells expressing NK receptors are believed to play key roles in patrolling, surveying, and destroying cells with an abnormal phenotype as a result of stress or infection [34]. In IL-2 and IL-12 rich microenvironments, CD56 expression was induced from γδ T cells, which exerted potent cytotoxicity [35]. Because IL-12 is reported to increase in the eyes with active uveitis [36], the intraocular γδ+CD56+ T cells from patients with Behçet's uveitis may act as cytotoxic effectors like CD8+CD56+ T cells.

The predominance of CD8+ T cells can be in part explained by the expansion of CD8+CD56+ cells. However, CD8+CD56- cells were also increased in Behçet's uveitis patients. The CD8+ T cell dominancy might be related to the chronic and massive tissue destruction observed in Behçet's uveitis. In type I diabetes, which is a prototype CD4+ T cell mediated autoimmune disease, tissue destruction is dominated by CD8+ T cells in the chronic stage [37]. Additional studies on the putative mechanisms underlying these abnormalities are required.

The different population of CD14+ monocytes also requires some comments. The monocytes, being important antigen-presenting cells (APC), tend to increase in both the aqueous humor and the peripheral blood of patients with Behçet's uveitis and VKH syndromes, which are characterized by the involvement of the posterior segment of the eye. The increase of monocyte in these uveitis syndromes may be connected with the chronicity or the involvement of viral or bacterial antigens in the pathogenesis; however, in this study, the duration of disease was not so different among the groups.

In summary, the CD8+ T cells were prominent in the aqueous humor of the patients with Behçet's uveitis, whereas CD4+ T cells were mainly found in the aqueous humor of patients other than those with Behçet's uveitis. The number of NKT cells was significantly higher in Behçet's uveitis than the other groups; CD8+CD56+ cells was the predominant subtype of the increased NKT cells. These results suggest that the immunopathogenesis of endogenous uveitis is somewhat different, and that CD8+CD56+ NKT cells may play an important role in the immunopathogenesis of Behçet's uveitis. The identification and analysis of the T lymphocytes from the aqueous humor can assist in understanding the roles of the infiltrating T cells in the pathogenesis of the different subsets of uveitis. This information may help to characterize the pathogenesis, and provide a differential diagnosis of the various types of chronic uveitis.

Acknowledgments

This study was supported in part by the grant (03-2000-021) from Seoul National University Hospital.

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