Fig. 4. Platelet-secreted PAF stimulates MC degranulation in vivo.

(A) Temperature measurement following intravenous administration of collagen and epinephrine with (CollE WEB) or without (CollE) pretreatment with the PAF inhibitor WEB2086; control animals received intravenous phosphate-buffered saline (PBS). Administration of anti–integrin aIIb (MWReg30) antibody caused significant thrombocytopenia [representative anti-glycoprotein IX (GPIX) stain versus forward scatter (FSC) before (B) and after (C) treatment]. (D) Temperature measurement following intravenous administration of MWReg30 in untreated mice (WT), in WEB2086-pretreated (WT-WEB) and platelet-depleted (WT-PLT deplete) mice, and in phospholipase A2–(Pla2-KO) and PAF receptor–(Pafr-KO) knockout animals. (E) Temperature measurement after administration of purified PAF (2 mg/g bodyweight) in WT, Pla2, or Pafr-knockout (Pafr-KO) mice. Adoptive platelet transfer was performed in hIL-4Rα/GPIbα–transgenic mice. These were platelet-depleted through administration of anti–IL-4R antibody (F) and repleted with platelets from either Pla2-KO or WT mice (G) before administration of MWReg30 (H). Fluorescence-activated cell sorting (FACS) data are shown as anti-GPIX stain versus forward scatter and is representative of experimental findings. Systemic response to MWReg30 was measured as change in body temperature (I) and by quantification of plasma levels of MC-specific chymase (J) and TNFα (K). Data are represented as the means ± SD. n = 4 to 6 per condition. *P < 0.05 versus control-treated animals and #P <0.05 versus respective stimulated WT or WT-repleted animals. (A, B, and G) Two-way ANOVA; (H and I) one-way ANOVA and Tukey’s multiple comparisons test.