Platelet aggregation and cryo-IgM in the study of hepatitis and immune complex states.

Hepatitis and other sera were studied for direct platelet aggregating (P1.A.) activity in non-heated and heat-treated state, for inhibitability of P1.A. by antiglobulin active cryoglobulin IgM components (Cryo-IgM), and for sedimentation velocity of P1.A. activity by sucrose gradient centrifugation. Three distinct patterns of direct P1.A. activity were established: (1) aggregated IgG type': heating-dependent, [unk]19S, inhibitable by Cryo-IgM, serum anticomplementary; (2) antibody type': heating-independent, 7S and/or 19S, non-inhibitable by Cryo-IgM, serum not anticomplementary; and (3) `immune-complex type': heating-independent, [unk]19S, inhibitable by Cryo-IgM, anticomplementary activity present or absent. In the heavy P1.A.-active sucrose gradient serum fractions of one patient, only IgG4 Gm markers were detected.