TABLE 1.
T-CELL AND NK CELL SUBSETS INVOLVED IN LUNG HOST DEFENSES
| Characteristic | αβ T cells | γδ T cells | NK T cells | Classical NK cells |
|---|---|---|---|---|
| TCR variable chains | αβ | γδ | αβ | None |
| MHC restriction | Class I or II | Class IB (some) | CD1d | Class I (suppresses) |
| Expressed TCR diversity | Large | Limited | Limited | None |
| Antigen recognition | Peptide plus MHC | Protein, unusual nonproteins | α-galactosyl ceramide, self-glycolipids | Multiple activation receptors sensing cellular stress |
| Phenotype | CD4+ or CD8+ | Mostly CD4−, CD8− (CD8 αα+ in gut) | CD4+ or CD4−, CD8− | CD4−, CD8− |
| Frequency in blood (% of lymphocytes) | 65–70% | 1–5% | 0.01–1% | 5–7% |
| Distribution in absence of inflammation | Blood and lymphoid tissue | Epithelia, blood | Liver, spleen, bone marrow | Blood, spleen |
| Autoreactivity | Only in TR subset | Yes | Yes | No |
| Effector functions | Cytokine release (Th1/Th2) Cytolysis (mostly CD8+) | Cytolysis Cytokine release (Th1 > Th2) | Cytolysis Cytokine release (Th1 > Th2) | Cytolysis |
| Principal roles in lung defense | Immunoregulation, cytokine secretion | Immunoregulation, immunosurveillance | Polarization of immune responses | Immunoregulation, Lysis of virally infected cells |
Adapted from data in or cited by References 13, 14, 18, 35.