Figure 2. The MT is a well-characterized model of a memory immune response.

Samples were collected between 0 and 19 days after PPD injection. (A) Skin biopsies were collected for immunohistochemistry (top panel), and cutaneous lymphocytes were isolated from skin suction blisters that were induced over the sites of PPD injection at different time points (lower panel). (B) PPD-specific memory T cells accumulate during the course of MT. PBMCs and blister cells were stimulated with PPD for 15 hours in the presence of Brefeldin A and stained for intracellular expression of IFN-γ (right y axis, solid lines). The number of CD3⁺ T cells within dermal perivascular infiltrates was determined by indirect immunoperoxidase staining of 5-μm tissue sections. The 5 largest perivascular infiltrates were counted and data presented per unit area (UA). The mean ± SEM of 5 individuals per time point is shown (dashed line, left y axis). (C) Blister cells recovered from day 7 blisters were stimulated with PPD or with irrelevant antigen (HSV, CMV, tetanus) or left unstimulated and stained for intracellular expression of IFN-γ. Representative dot plots (n = 3 samples per antigen) are shown. Numbers denote the percentage of cells expressing IFN-γ. (D) IFN-γ production from day 7 blisters raised over MT response or the site of the control (saline) injection. Numbers denote the percentage of cells expressing IFN-γ. PBMCs and blister cells (PPD and control) from the same donor were stimulated with PPD overnight as described in Methods.