The mechanism of thrombocytopenia associated with mumps was investigated in a case proved by virus isolation. Although an immune mechanism for the thrombocytopenia has been postulated, platelet agglutinins, clot retraction inhibitors, complement-fixing platelet antibodies, or stimulation of platelet factor 3 availability could not be demonstrated in either the presence or absence of mumps-specific antigens. These results suggest that thrombocytopenia is not a consequence of antibodies directed against normal platelets nor against mumps antigen adsorbed to platelets. Rather, it appears that in this disorder, thrombocytopenia may result from a direct action of the virus or a viral antigen-antibody complex on platelets.
Graham DY, Brown CH, Benrey J, Butel JS. ThrombocytopeniaA Complication of Mumps. JAMA. 1974;227(10):1162–1164. doi:10.1001/jama.1974.03230230038021