In vitro induction of suppressor cells by plasma of rats with Trypanosoma brucei rhodesiense infection.

Mitogenic responses of B and T lymphocytes from spleens of rats infected with Trypanosoma brucei rhodesiense were suppressed. Plasma from infected rats suppressed the mitogenic responses of B and T lymphocytes from spleens of normal uninfected rats. Removal of immune complexes from plasma of infected rats significantly reduced the suppressive effect of the plasma on splenic lymphocytes of normal uninfected rats. Normal thymus cells treated with plasma from infected rats and added to cultures of normal spleen lymphocytes inhibited the mitogenic responses of B and T lymphocytes. We suggest that the interaction of immune complexes and Fc or C3b receptors of T lymphocytes resulted in the in vitro induction or activation of T suppressor lymphocytes.

Reversal of immunosuppression induced with plasma of malarious rats by supplemented complement.

Suppression of antibody producing splenic lymphocytes by plasma from rats infected with Plasmodium chabaudi malaria was confirmed. Suppressive activity was found in plasma drawn on the sixth, seventh and eighth day of infection. It was temporally associated with anemia, elevated levels of soluble immune complex, reduced titers of lytic complement and elevated titers of immunoconglutinin (IK) in the plasma. Heat inactivation of the plasma to destroy complement and removal of IK by absorption did not reduce the suppressive activity. Incubating the plasma-treated lymphocytes with normal rat complement largely, but not completely, reversed the suppressive action. Soluble immune complexes prepared from bovine serum albumin (BSA) and antiBSA (BSA-antiBSA) alexinated complex (BSA-antiBSA-C') and immunoconglutinated complex (BSA-antiBSA-C'-IK) each suppressed the capacity of splenic lymphocytes from rats immunized with sheep blood cells to produce hemolytic Jerne plaques. Incubating the complex-treated cells with fresh complement largely reversed the suppressive activity. It is suggested that the suppressed responses of lymphocytes from malarious animals to antigens or mitogens, reported by others, may have been in part induced by complexes in blood of the animals, and that antibody producing cells might also have been suppressed. Since suppressive activity was not influenced by complement inactivation, but was reversed when plasma-treated cells were incubated with fresh complement, it is suggested that the hypocomplementemic state of suppressive plasma may have contributed to immunosuppression.

Complement reversal of immunosuppression induced with plasma of rats infected with Trypanosoma brucei rhodesiense.

Suppression of antibody production by splenic lymphocytes from rats immunized with sheep red blood cells (SRBC) after incubation with plasma from rats infected with Trypanosoma brucei rhodesiense was confirmed. Suppressive activity became evident in plasma after the sixth day of infection and was manifested by reduction in the number of hemolytic Jerne plaques produced by the treated cells. The activity was temporally associated with increased amounts of soluble immune complex (SIC) reduced titers of lytic complement, elevated titers of immunoconglutinin (IK) and anemia. Treatment of suppressive plasma with hemolysin sensitized SRBC alexinated with horse complement to reduce IK did not reduce suppressive activity, and the activity appeared to have been enhanced when the plasma was heated to inactivate the remaining complement (C'). When fresh rat C' was added to the treated cells, the suppression was largely, though not completely, reversed. Treatment of spleen cells with SIC prepared in vitro from bovine serum albumin (BSA) and rabbit antiBSA also suppressed the plaque forming capacity of the cells. Complexes of BSA-antiBSA-C' and complexes of BSA-antiBSA-C'-IK were equally suppressive. Again, addition of fresh C' to cells treated with these complexes largely, though not completely, reversed the suppressive effect on the cells. From the results it is suggested that immunosuppression associated with experimental T. b. rhodesiense infection may be in part a suppression of the capacity of induced lymphocytes to produce antibody. It is possible that the suppression was mediated by SIC present in the plasma of the infected rats and this effect was probably enhanced by reduced levels of complement in the suppressive plasma.

Wool production of sheep chronically infected with Haemonchus contortus.

A chronic infection was established in a group of twenty 18-month-old non-reproductive Merino ewes by oral administration of 3000 infective H. contortus larvae twice weekly for 12 weeks. Their live-weights and wool production were compared with those of 20 uninfected ewes grazing the same pasture. In the infected sheep, faecal egg counts increased over a period of 9 weeks to reach a mean of 5000 eggs per gram, accompanied by small, but significant effects on packed-cell volume and live-weight. The effects of infection on wool growth were also small, and not statistically significant, although there was evidence of a faster seasonal decline in wool growth in infected sheep. It was concluded that mortality induced by acute infection is the most important economic effect of this parasite.

Immunoconglutinin and suppression of an induced immune response by plasma from rats infected with Trypanosoma brucei rhodesiense.

Fresh plasma from rats infected with Trypanosoma brucei rhodesiense, incubated with splenic lymphocytes from rats previously immunized with sheep blood cells, suppressed the capacity of the splenic lymphocytes to produce antibody as was indicated by reductions in the numbers of hemolytic Jerne plaques produced by the treated cells. The effect was maximal in plasma samples drawn on the sixth to eighth day of infection when they contained elevated amounts of soluble immune complex, high titers of immunoconglutinin (IK), and reduced titers of lytic complement. We suggest that the active plasma may have affected the antibody-producing cells by one or both of two mechanisms. Soluble antigen-antibody complexes may have interacted with Fc receptors of activated lymphocytes to suppress antibody production. Alternatively, complement-fixing soluble immune complexes may have reacted with C3b receptors of the lymphocytes. These lymphocytes coated with the antigen for IK could then be injured by immunoconglutination.

Immune complexes and immunoconglutinin interactions associated with altered lymphocyte activity in Plasmodium chabaudi infections.

Fresh plasma from rats infected with Plasmodium chabaudi, incubated with splenic lymphocytes from rats immunized 5 days previously with sheep blood cells, suppressed the capacity of the spleen cells to produce antibody against the sheep cells as was indicated by reductions in the numbers of hemolytic Jerne plaques formed by the treated cells. The effect was maximal in plasma of rats drawn on the 7th day of infection at a time the rats experienced a hemolytic crisis. Serologic studies indicated that the active plasma contained elevated titers of antibody against fibrinogen products, antibody against the soluble serum antigens elaborated during blood infections and antibody against the third component of fixed complement (C3) or immunoconglutinin. Titers of lytic complement were reduced and amounts of soluble immune complex precipitated with polyethylene glycol 6000 were elevated. The active plasma may have affected the antibody producing cells by one or both of two mechanisms. Soluble antigen-antibody complexes could have interacted with Fc receptors of activated lymphocytes to alter their function. Alternatively, the complexes may have fixed complement and interacted with receptors for fixed C3 on the lymphocyte membrane. Such cells, being coated with the antigen for immunoconglutinin, could be altered by immunoconglutination. Inasmuch as the immune complexes in the active plasma were generated in vivo, it would seem unlikely that the plasma would contain significant amounts of complex that had not fixed complement. With immunoconglutinin present in the plasma, alteration of the cells by immunoconglutination seems a more likely possibility.

Anemia and thrombocytopenia from Corynebacterium parvum-stimulated resistance against malaria, trypanosomiasis, and babesiosis.

Nonspecific immunity (NSI) was manifested in rats injected intravenously with killed Corynebacterium parvum and challenged with Trypanosoma lewisi, Plasmodium chabaudi, or Babesia rodhaini. The NSI became evident some 5 days after infection as a suppressed parasitemia, a more rapid recovery from patent infection and as enhanced survival among rats infected with B. rodhaini. The C. parvum injections produced anemia and thrombocytopenia with splenomegaly and signs of glomerulonephritis in rats. The signs became evident about 5 days after injection and were accompanied by reduced titers of lytic complement, elevated titers of antibody against fibrinogen products (Anti-F), antibody against soluble serum antigen of malaria and babesiosis (ABSA), and antibody against the third component of fixed complement or immunoconglutinin (IK). These were the autoantibodies associated with anemia and reduced parasitemia of infection-induced NSI. In as much as immunoconglutination of blood cells or parasites coated with complement fixing immune complexes was implicated as a functional mechanism in infection-induced NSI, it is possible that these same factors might function in C. parvum induced NSI.

Interrelationships of immunoconglutinin, immune complexes, and complement in anemia, thrombocytopenia, and parasitemia of acute and chronic malaria in rats.

Anemia, thrombocytopenia and reduction in parasitemia in P. chabaudi infection of rats were associated with appearance in blood of soluble immune complexes, immunoconglutinin (IK), and by reductions in titers of lytic complement. With reduction of parasitemia to subpatent levels, anemia, but not thrombocytopenia, persisted and erythrocyte counts did not return to preinfection levels for several weeks. This chronic anemia was accompanied by elevated amounts of soluble immune complex, depressed titers of lytic complement and persistence of IK. Evidence was presented indicating that the infections of the rats persisted in a chronic form. It was thus indicated that immune interactions, related to anemia and clearance of parasitemia, persisted in absence of microscopically evident parasitemia, and may have been in part responsible for the persistent anemia. Based on the evidence cited, it is suggested that complement-fixing immune complexes attach to blood cells, infected as well as uninfected, and that these cells are sequestered and phagocytized in the spleen after immunoconglutination by IK. It is also suggested that this interaction continued after the clearance of patent parasitemia and accounted for the persistence of anemia in the chronic phase of infection.

Immunoconglutinin and antibody against fibrinogen products in hemolytic anemia and nephritis resulting from infection with a Haemobartonella-like agent.

An agent morphologically similar to Haemobartonella muris was isolated from the blood of rats infected with a strain of Trypanosoma lewisi kept at this Department. It caused acute hemolytic anemia, splenomegaly, glomerulonephritis, and death within 5 to 8 days in mature Sprague-Dawley rats. The disease was less severe in weanling rats which usually recovered within 3 to 4 wk. The anemia was accompanied by phagocytosis of erythrocytes by monocytes of the spleen and bone marrow, by high titers of cold-active hemagglutinin, high titers of antibody to the third component of fixed complement (immunoconglutinin), and antibody to fibrinogen/fibrin related products. Filtrates of blood from anemic rats passing a 0.20-micron filter did not produce disease or signs of infections, but filtrate from a 0.45-micron filter was infective. Attempts to grow the agent on rat embryo fibroblast cultures and in embryonated chicken eggs were successful. Tests for bacteria, mycoplasma, and spirochetes gave negative results. Blood of infected rats did not produce signs of infections when inoculated into laboratory mice, and normal rats housed in cages with acutely infected rats did not develop signs of infection or disease. Morphological similarity did not allow differentiation of the agent from H. muris. However, its virulence for mature rats differs markedly from that usually seen in H. muris infection.

Immunologic reactions associated with anemia, thrombocytopenia, and coagulopathy in experimental African trypanosomiasis.

Rats infected with Trypanosoma brucei rhodesiense developed anemia, thrombocytopenia, and hypocomplementemia. Anemia, thrombocytopenia, and sharp reductions in parasitemia were associated with elevated titers of cold-active hemagglutinin, antibody to fibrinogen/fibrin-related products, and immunoconglutinin. Depletion of lytic complement, prolonged partial thromboplastin times, and presence of fibrin monomers in the blood occurred at the time anemia and significant elevations in precipitable immune complexes were observed. Terminally, consumption of immunologic factors coincided with accelerated partial thromboplastin times. At death, convulsions and hemoptysis with labored breathing suggested that the animals died of respiratory failure and that disseminated intravascular coagulation may have occurred. It is suggested that microthrombiosis might have resulted from the immunologic interaction of complex-coated blood cells with immunoconglutinin and contributed to the terminal disease signs.

Antibody to fibrinogen/fibrin products (Anti-F) in malaria, babesiosis, and trypanosomiasis of rodents.

Antibody to fibrinogen/fibrin related products (Anti-F) was stimulated during the course of Plasmodium chabaudi, Babesia rodhaini, and Trypanosoma lewisi infections in rats. Titers of this autoantibody remained elevated in serum from rats that had recovered from each of the infections. Column chromatographic studies indicated that Anti-F was a 19S globulin, possibly IgM. During acute infections high titers of Anti-F were associated with elevated titers of cold-active hemagglutinin (CAH) and immunoconglutinin (IK) and all were associated with anemia and elevated parasitemia. Titers of Anti-F and IK, but not CAH, remained elevated in serum of recovered rats. The presence of Anti-F indicated that the coagulation system had been activated during each infection to release fibrinogen/fibrin-related products (FRP) to serve as antigen(s) for Anti-F. Since IK is antibody to the third component of fixed complement, it could be assumed that complement fixing antigen-antibody complexes were also present during the acute stage of each infection. The possibility that complexes of FRP and Anti-F could have contributed to anemia in each infection is discussed.

Association of autoantibodies with anemia, splenomegaly, and glomerulonephritis in experimental African trypanosomiasis.

Rats experimentally infected with Trypanosoma brucei rhodesiense developed a syndrome characterized by anemia, splenomegaly, and glomerulonephritis. Serologic evaluation revealed that the syndrome was accompanied by the presence of 3 autoantibodies--cold-active hemagglutinin, immunoconglutinin, and antibody to fibrinogen/fibrin products. Fluorescein isothiocyanate conjugated antibody tests showed the presence of fixed complement and fibrinogen on both trypanosomes and erythrocytes. All infected rats died by the ninth day of the infection with 5 animals showing signs of pulmonary involvement and shock. From these observations it is suggested that autoantigens, autoantibodies, and complement may have been causal in this syndrome.

Immunoconglutinin associated with nonspecific acquired resistance in malaria, babesiosis, and other anemia-inducing infections.

Rats recovered from infectious anemias had an acquired nonspecific resistance. Recovery from trypanosomal and babesial infections enhanced the resistance to infections with filterable rat infectious anemia (RIA) agent, and recovery from RIA made rats more resistant to plasmodial, babesial and trypanosomal infections. The resistance was manifested after challenge by reduced parasitemia accompanied by significant anemia, which became evident 2 or 3 days earlier in recovered rats than in controls. Mortality of the recovered rats was less than that of the controls. Immunoconglutinin (IK) was detected with high titers in animals during the acute stage of each infection and remained present with lower titers after recovery. After the recovered rats were challenged with a heterologous agent, the existing IK titers became elevated earlier and usually were higher than those of the controls. However, the infections also stimulated production of cold-active hemagglutinin (CAH). It was therefore not clear that the resistance could be attributed to IK. The nature of antigen-antibody complexes that may have fixed complement and stimulate IK is discussed. However, a specific complex was not implicated.

Anemia, splenomegaly, and glomerulonephritis associated with autoantibody in Trypanosoma lewisi infections.

Anemia with splenomegaly and signs of glomerulonephritis were found associated with the acute and post-acute phase of Trypanosoma lewisi infections of laboratory rats. The onset of the anemia was associated with the peak of parasitemia and the development of cold-active hemagglutinin (HA) for trypsinized rat erythrocytes. It persisted with gradual recovery for as long as the trypanosomes and HA were detected in the blood. Signs of glomerulonephritis consisted of hypercellularity of the glomerular tuft, swelling of vascular endothelium and tubular epithelium, thickening of Bowman's membrane and tubular basement membrane, and abnormal numbers of hyaline casts in the distal convoluted tubules. Residual damage to the kidneys was not evaluated.

Experimental infection with Plasmodium chabaudi in rats: antigen and antibody associated with anemia and glomerulonephritis of acute infection.

Rat-adapted Plasmodium chabaudi caused a syndrome characterized by hemolytic anemia, splenomegaly, and glomerulonephritis. All rats recovered and appeared normal after 4 weeks despite persistence of proteinuria. Serologic studies on the malarious rats revealed that the infection was associated with a soluble antigen which was present concurrently with antibody in plasma, in material eluted from blood cells, in extracts of kidney tissues, and in the urine. This antigen appeared to be identical with one extracted from P. chabaudi parasites and did not cross-react with antigens of Plasmodium gallinaceum. Tests for the cold-active hemagglutin (CAH) and the globulin associated serum antigen (SA) previously associated with acute malaria, revealed that CAH, but not SA, was present. From these observations it is suggested that soluble complexes of the parasite antigen and its antibody may have been causal in this syndrome.

Experimental infection with Plasmodium chabaudi in rats. Observations on adaptation and the immune responses to infection.

Plasmodium chabaudi was adapted to rats after some initial refractoriness. Progressive adaptation was indicated by shortening of the prepatent period and increases in peak parasitemia with successive passages. Rats infected with parasites of early passages resisted the infection, and even splenectomized rats quickly recovered. However, the parasites appeared to become more virulent with successive passages and after the 45th passage, all adult rats inoculated with the parasite died with severe hemolytic anemia. After adaptation, infections of the rat strain appeared to stimulate resistance in mice that was more effective against challenge with parasites of the homologous strain than it was against challenge with mouse strain parasites. Rats recovered from P. chabaudi were highly resistant to the homologous strain of P. chabaudi, but they were no more resistant to Babesia radhaini than were normal rats. However, when the rat strain was used to immunize mice, they were as resistant to B. rodhaini as they were to mouse strain P. chabaudi. Serologic studies made on rats with acute infection indicated that anemia was associated with antibody to erythrocytes as well as with high parasitemia. The soluble serum antigen (SA) associated with malarial and babesial infections was not present and its antibody was not detected in serum of recovered rats. However, antibody to SA was detected in blood mice that had recovered from rat strain P. chabaudi infection. Thus acquired resistance to B. rodhaini appeared to have been associated with elaboration of SA.