Reduced innate and adaptive immune cell populations in spleens of platelet-depleted infected animals correlates with an increase of necrotic splenocytes. Groups of mice were treated with PBS or 40 μg of anti-GPIIb antibody 12 hours before, and 2 and 4 days after LCMV Armstrong infection. (A) Splenic quantification of immune cells by flow cytometry. Collagenase-digested spleens of day 8 infected animals were quantified. (B) Detection and quantification of dead splenocytes. Flow cytometry analysis of day 8 postinfection splenocytes that were collagenase digested and stained with an in-house Alexa Fluor 430 dye protocol that detects disruptions of cell membranes. Top panel shows a representative histogram of the analysis gated on total splenocytes (gray histogram, untreated; empty histogram, depleted; numbers indicate percentage of positive cells). Bottom panel shows numbers of dead splenocytes. (C) Serum cytokine levels. Untreated and depleted animals were bled 24 hours after infection. Sera from each group were pooled and levels of 21 different circulating cytokines determined by a commercial immunoassay method with each cytokine detected in duplicate (n = 6). Bottom table shows the arrangement of the cytokines on the membranes, and 3 relevant cytokines (IL-17, IFNγ, and TNFα) were marked. (D) The absence of platelets, not the anti-GPIIb depletion protocol, is the defining factor. Mice were treated with PBS or with 2 different platelet-depleting reagents (anti-GPIbα or aspercetin), and serum viral titers were determined 8 days after infection. (A-B,D) Open bars, PBS-treated controls; black bars, platelet-depleted mice. Error bars represent SEM (*P < .05). NS indicates nonsignificant.