Exacerbation by viral infection of thrombocytopenia induced by polyclonal antibodies. (A) IgG (3 μg) purified from polyclonal anti-mouse platelet rabbit serum (anti-plt Ab) or control rabbit IgG was injected into groups of 4 CBA/Ht mice 1 day after LDV infection or administration of saline. Platelets were counted 2 days after antibody administration (○ represents each individual datum; •, means ± SEM). (B) Similar experiment performed in groups of 5 CBA/Ht mice after infection with MHV 1 day before administration of polyclonal antiplatelet or control antibodies.