Figure 5.

Circulating, activated platelets reconstitute CHS response in L-selectin–deficient mice. (A) Mice were sensitized to DNFB on day 0. CHS was elicited at day 5, and the subsequent ear swelling response was measured 24 h later. 18 h after sensitization, some animals were injected intravenously with TRAP-activated human platelets (3 × 10⁸ in 3 ml over 6 h). Some L-selectin^−/− animals were also treated with either P-selectin mAb WAPS 12.2 or CD31 mAb Hec 7. There was no significant difference between the response of L-selectin–deficient mice and wild-type mice which were elicited without earlier sensitization (P >0.05). Ear swelling in sensitized wild-type animals with or without platelet infusion was highly significant (P <0.001 versus elicit only). In sensitized L-selectin^−/− mice, elicitation alone had no effect, whereas mutant mice that also received activated platelets displayed a dramatic swelling response (P <0.001) that was not different from that in sensitized wild-type animals with or without platelet treatment (P >0.05 versus both). MAb Hec 7 had no significant effect (P >0.05 versus sensitized L-selectin^−/− receiving activated platelets only), whereas coinjection of platelets and MAb WAPS12.2 abolished the delayed type hypersensitivity effect (P >0.05 versus both L-selectin^−/− groups without platelet infusion; P <0.001 versus sensitized, platelet-treated L-selectin^−/− animals; P <0.01 versus sensitized, platelet plus MAb Hec 7–treated L-selectin^−/− animals). Data shown are mean ± SD from 4 to 11 mice in each group (5 measurements per ear before and after elicitation). (B) Antigen–specific T cells are present in PLN of L-selectin–deficient mice only after treatment with activated platelets. Cells from mice sensitized 5 d earlier with DNFB were cultured for 36 h in the presence of DNBS after which the cultures were pulsed with [³H]thymidine for 18 h. Each point represents the mean ± SD of three separate mouse groups, with each group consisting of pooled PLN from two mice. Each group was done in triplicate. Background proliferation was subtracted as previously described (7). (C) Magnitude of CHS response in L-selectin–deficient mice receiving activated platelets correlates with the number of resident lymphocytes in PLN. After eliciting a CHS response, six PLN per mouse (subiliac, axillary, and cervical) were harvested and the number of resident cells was counted and correlated to the extent of the ear swelling. PLN were obtained from mice which had received no platelets (n = 5), activated platelets (n = 11), activated platelets pretreated with control mAb Hec 7 (n = 4), or activated platelets pretreated with mAb WAPS 12.2 (n = 5).