Blood cells from rats infected with Trypanosoma brucei rhodesiense agglutinated when cooled in an ice bath and dissociated when warmed to 20 C. This autohemagglutination was seen when reduced erythrocyte and parasite counts became evident. Pools of plasma from rats showing the reaction agglutinated normal rat blood cells (NRBC) and sheep red blood cells (SRBC) at similar titers at 4 C, and the agglutinated cells dissociated at 20 C. The active plasma contained elevated titers of cold-active hemagglutinin (CAH) detected with trypsinized erythrocytes, immunoconglutinin (IK), and antibody against fibrinogen products (Anti-F). The quantity of precipitable, soluble, immune complex (SIC) was elevated. Absorption of the plasma with NRBC and SRBC at 4 C reduced the autohemagglutination activity and reduced titers of CAH, IK, Anti-F, and the quantity of SIC. Hemagglutination and each of the serologic activities, except CAH, were detected in eluates of the blood cells used for absorption. Specificity of CAH was shown to be for erythrocyte stroma. Because CAH was not found in the eluates, it appeared that this autoantibody had no role in the observed autohemagglutination activity. Heat-inactivated plasma did not agglutinate SRBC at 37 C, suggesting that heterophile antibody was not involved. Because IK, Anti-F, and SIC were recovered from the cells used for absorption and the eluate from the cells agglutinated NRBC and SRBC at 4 C, we suggest that those factors had interacted at 4 C to agglutinate the cells. We propose that SIC, including complexes of fibrinogen products and Anti-F, had fixed complement, became bound to the blood cells, and that cells were conglutinated by IK. We also suggest that this phenomenon of panautohemagglutination, which may be associated with a variety of infectious diseases, actually may be a cold-active immunoconglutination. We reported that rats infected with Trypanosoma brucei rhodesiense developed a syndrome of anemia with thrombocytopenia, splenomegaly, and glomerulonephritis accompanied by coagulation abnormalities. Onset of the signs, with a hypoclottable state, was associated with appearance in the blood of antibody against the third component of fixed complement or immunoconglutinin (IK), cold-active hemagglutinin detected with trypsinized blood cells, Anti-F (an antibody against fibrinogen/fibrin products), and by a reduction in titers of lytic complement. Terminal signs, which resembled those of pulmonary thrombosis or disseminated intravascular coagulation (DIC), were accompanied by consumption of Anti-F and IK and absence of lytic complement. Blood drawn to anticoagulant at or near the time of the terminal crisis appeared to clot as it cooled. Therefore, it was suspected that this apparent clotting Received 13 October 1980; accepted 9 January 1981. * Address reprint requests to Herbert W. Cox. t Present address: Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, 5, Thailand. might be relatable to the phenomenon of cold autohemagglutination described by Yorke (1911) in clinical trypanosomiasis (Rickman and Cox, 1979, 1980). From the studies of Rickman and Cox (1979), it was perceived that complement-fixing immune complexes became bound to blood cells and trypanosomes. Because the cells were coated with the antigen for IKi.e., complement-fixing immune complexthey could be conglutinated by IK. We report here studies on blood drawn from rats on various days during the course of T. b. rhodesiense infection. Tests for autohemagglutination became positive at the time that anemia became evident. Plasma samples that agglutinated homologous normal blood cells contained high titers of IK, cold-active hemagglutinin (CAH), Anti-F, and immune complexes. Eluates from agglutinated cells, agglutinated normal rat erythrocytes at 2 C. Serologic study indicated the eluates contained Anti-F, IK, and soluble immune complexes. MATERIALS AND METHODS Experimental animals and infection Sprague-Dawley rats and the T. b. rhodesiense infection were from sources described by Rickman
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