Formation of platelet-binding antibodies in response to IV ChAdOx1 nCov-19 application. (A) Spleen weights of animals 6 days after inoculation. Representative images of spleens of both groups are shown; scale bar is 2 cm. Unpaired t test. n = 5 per group. (B) Quantification of B220⁺ are in the spleen of IV or IM ChAdOx1 nCov-19–injected mice 6 days after inoculation as percentage of total splenic area. Unpaired t test; n = 3 per group. Representative images of a splenic micrograph of both groups are shown; scale bar is 100 µm. (C) Control mouse platelets positive for bound IgM and IgG after incubation with plasma from mice 6 days after inoculation with either IM or IV ChAdOx1 nCov-19 or ChAdOx1 nCov-19 AID^−/−sIgM^−/− mice for IgG additionally. n = 5 per group for IV or IM; n = 4 for AID^−/−sIgM^−/−. Unpaired t tests between IV ChAdOx1 nCov-19 and the other groups. Percent of platelets binding IgM or IgG are normalized to the mean of 4 control plasmas. Error bars are mean ± SEM. *P < .05; **P < .01; ***P < .001.