MODULATION OF ANTI-SHEEP ERYTHROCYTE PRIMARY ANTIBODY-RESPONSE BY PROTEIN A IN NORMAL MICE

Protein A (PA), a cell wall glycoprotein of Staphylococcus aureus Cowa n I, is known to possess immunomodulatory and antitumor activities. In the present study the effect of protein A on the anti-sheep erythrocy te primary antibody response in normal mice has been investigated. Int raperitoneal administration of PA resulted in suppression of primary a ntibody response in mice immunized with sheep red blood cells (SRBC) a s assessed by plaque forming cell (PFC) assay. The suppressive effect was dose dependent. Maximum suppression in PFC response was observed a t 12 mu g PA/animal and could be observed as low as 1 mu g PA/animal. The suppression at 6 and 12 mu g PA/animal was significant when compar ed with control values (p<0.02 and p<0.001, respectively). However, no significant suppression was recorded at 1 mu g dose. The suppression was proportional to the numbers of administrations of PA to the mice a nd critically dependent on the timing of inoculation of PA. PA produce d pronounced suppression when injected prior to the immunization of an imals with SRBC. PA reduced splenic localization of Cr-51 labelled SRB C to 55%. It is proposed that the altered localization of antigen (SRB C) in spleen may be responsible for reduced plaque forming cells in no rmal mice.