Platelet response to acute SIV infection in singly compared with socially housed macaques. Housing groups were compared at baseline (two time points) against day 10 after inoculation with SIV (for n for each time point, see Supplemental Digital Content, Table S4, http://links.lww.com/PSYMED/A873). ART was started on day 12 for all animals. A, Platelet counts in whole blood CBCs were compared. Singly housed animals showed a delayed recovery from thrombocytopenia during acute infection, failing to return to baseline by day 14. Differences between housing groups over time were significant (F(4,64) = 8.26, p < .001). B, Platelet P-selectin expression in singly housed macaques was less than in socially housed both at baseline and at day 10. C, The effects of housing (F(2,41) = 47.03, p < .001) and housing over time (F(2,41) = 53.29, p = .009) were significant. Platelet CD40L expression was not different between groups at day 10; however, a difference was present in a single baseline time point. In addition, the effect of housing over time was significant (F(2,41) = 10.03, p < .001). D, Platelet MHC-I expression was not as upregulated at day 10 in singly housed animals. In addition, the effect of housing over time was significant (F(2,39) = 4.18, p = .023). Error bars display the standard error of estimated least squares means generated by a linear mixed-effects regression model. * p < .05; ** p < .01; *** p < .001. SIV = simian immunodeficiency virus; ART = antiretroviral therapy; CBC = complete blood count.