Eperythrozoon coccoides. II. Effect on interferon production and role of humoral antibody in host resistance.

Eperythrozoon coccoides was shown to inhibit the interferon response in mice only during the first 3 weeks after acute infection. By 6 weeks the production of interferon in response to Newcastle disease virus returned to a normal level. Antibody to E. coccoides could be demonstrated by three methods: (i) neutralization, (ii) indirect fluorescent antibody, and (iii) gel diffusion. The clearance of the parasitemia could be correlated with the appearance of circulating antibody. The critical role of humoral antibody was confirmed by evidence that immunosuppressive therapy prevented, in an infected animal, clearing of E. coccoides from the blood and converted a nonlethal infection to one with a 100% mortality. Administration of immune serum to the E. coccoides-infected, immunosuppressed animal, however, resulted in clearing of the parasitemia and prevention of death. Finally, a series of immunosuppressive regimens failed to exacerbate E. coccoides in animals after recovery from the acute phase of infection. E. coccoides may not be as important a laboratory contaminant as postulated originally.