Rosette-forming cells during immune response to Toxoplasma gondii in mice

Abstract

The rosette-forming cell (RFC) response of mice immunized with varying doses of Toxoplasma gondii was studied by immunocytoadherence (ICA). The specificity of ICA in the present system was tested by passive sensitization with hyperimmune serum in vivo and in vitro. A slight increase in RFC was observed with the latter. Prior treatment of spleen cells from immunized animals with rabbit anti-mouse immunoglobulin resulted in total inhibition of ICA. During the primary and the secondary response after 10 days, the number of RFC rose rapidly to reach the peak on the 3rd day. With secondary immunization 30 days later, the peak shifted to the 2nd day. Mice infected with a lower dose of Toxoplasma had a greater number of RFC during the secondary response after 10 days than with a larger dose.The production of antibody at the cellular level can be studied by immunocytoadherence (ICA). This phenomenon is based on adherence in a cluster or "rosette" formation of a particulate antigen due to its binding the receptor sites around a lymphoid cell. The method of localized hemolysis in gel (19) can also be used for this. However, a comparision of these two techniques has shown ICA to be more sensitive (40). It was introduced for detecting cells producing anti-erythrocyte antibody, and the term ICA was coined for it (25). It is of interest to note that similar adherence had reportedly been observed earlier in this century with protozoan parasites, Trypanosoma, and Leishmania (24), and the occurrence of ICA has been demonstrated more recently for trypanosomes (11).The many applications of ICA include cytodynamic studies of the immune response (6, 35), evaluation of drugs used as immunosuppressants (2), studies of time of transplantation rejection (3), determining drug hypersensitivity (28), as a diagnostic tool in sporotrichosis and histoplasmosis (30,31), and in correlating cell-mediated immunity estimated as delayedtype hypersensitivity (34).The immune response to Toxoplasma gondii, a coccidian protozoan, has been studied in depth at the humoral level by measurement of circulating serum antibody. However, there has been no attempt to investigate antibody production of this parasite at a basic cellular level. The present report deals with this aspect by applying ICA. MATERIALS AND METHODSPreparation of Toxoplasma suspensions. The BK strain maintained by regular intraperitoneal passage in mice was used. Parasites were harvested by washing out the peritoneal cavity with 2 ml of phosphate-buffered saline (PBS), pH 7.2. Exudate was collected on the 3rd day of infection or on the 5th day if brain homogenate was injected. Toxoplasmas were separated from the mouse peritoneal cells by a simple paper filtration method (22). Briefly, the exudate was diluted to contain 5 x 106 organisms per ml. Two milliliters of this was filtered through a fluted no. 5892 filter paper (Schleicher and Schull, Dassel, West Germany) and washed with an equal volume of PBS. Each filter was used twice, and the parasites from pooled filtrates were pelleted down b...

Immunomodulating effects of Toxoplasma gondii occur at an early stage of infection

“…In an earlier study from our laboratory, animals immunized for 24 h with formalin-treated toxoplasma demonstrated an increase in the number of antigen-binding cells as detected by the rosette formation of tachyzoites around the splenocytes [13]. Depletion of adherent cells from the spleen suspension showed that a considerable proportion of the total rosettes was formed by the adherent cells [14].…”