Figure 2. Primary cellular immune responses are delayed in mice lacking the thymus but T cell memory responses are maintained.

(A) Delayed Type Hypersensitivity (DTH) responses to ovalbumin in control (C), sham-operated (S) or athymic (T) mice. DTH responses to intradermic injection of 20 μg ovalbumin were examined in the footpad of mice 6 days after priming by subcutaneous injection with 100 μg of ovalbumin (priming) or PBS (control). Footpad swelling measured in mm is indicated on the y-axis. Mice lacking the thymus produced significantly larger swelling (15 mm, on average) in response to challenge than sham-operated mice (6.0 mm, on average) or control mice (6.5 mm, on average). Footpad swelling was compared by a paired two-tailed T test. (B) Kaplan Meier survival curves for H-Y incompatible skin grafts in athymic (T), sham-operated (S) or control (C) mice. x-axis, days following surgery; y-axis, skin graft survival fraction. Grafts were considered rejected when 90% or more of the graft lacked any viable signs: hair, pigment and scale pattern. The median survival time of first set grafts was 25 days in control mice, 25 days in sham-operated mice and 37 days in mice lacking the thymus. Skin graft rejection by athymic mice was significantly delayed compared to rejection in controls (p=0.0052, log-rank, Mantel-Cox test). Secondary transplants were done 8 to 12 weeks after rejection of the first transplant. The median survival time of initial transplants was 15 days in control mice, 16 days in sham-operated mice and 19 days in athymic mice. Secondary graft survival in athymic recipients did not significantly differ from graft survival in control or sham-operated recipients.