Analysis of immunosuppression during early acute infection of mice with Ascaris suum.

Immunosuppression was examined at 10 to 12 days following oral inoculation of 10,000 to 12,000 embryonated Ascaris suum eggs. Reduced antibody responses to sheep red cells (SRC) following systemic immunization were confirmed in CD-1 and C57Bl/6 mice. Infection alone induced antibody reactive with DNP equivalent to that observed after immunization with DNP--Ficoll. There was a decrease in thymus and spleen size by day 8 of infection, followed by a splenic proliferative response during the second week. In the second week, serum antibodies reactive with SRC, chicken erythrocytes, DNP and bacterial lipopolysaccharide were demonstrated, suggesting polyclonal B-cell stimulation. The cellular basis of immunosuppression was investigated by in vitro culture of splenocytes from C57Bl/6 mice. Differential leucocyte counts of splenocytes before culture demonstrated a relative increase in plasma cells, blastoid cells, complement receptor-bearing lymphocytes and eosinophils, with a relative decrease in small lymphocytes. The splenocytes had reduced responses to T-cell mitogens, as measured by thymidine incorporation in vitro, and reduced antibody responses to SRC and DNP--Ficoll. In vitro, cell mixing experiments did not demonstrate suppressor cells in the spleens of infected mice.