Variations in sheep serum conglutinating complement activity and pathway involved in reactivity with sheep...

Based on conglutination tests with the sheep E-rabbit A indicator system, three types of sheep sera were encountered. Type 1 sera failed to directly conglutinate or sensitize sheep E-rabbit A for conglutination by bovine conglutinin. Type 2 sera also failed to directly conglutinate sheep E-rabbit A but sensitized the indicator for conglutination by bovine conglutinin. Type 3 sera both directly conglutinated and sensitized sheep E-rabbit A for conglutination. Changes in serum type were induced in sheep by venepuncture (type 1 to type 2) or venepuncture and an intraperitoneal injection of yeast cells (type 2 to type 3). Direct conglutinating activity of type 3 sera was inhibited by heating serum at 50 degrees C for 30 min and was not restored by alternative activation pathway factor B. Chelation of Ca2+ in type 2 and 3 sera blocked sensitization of sheep E-rabbit A for conglutination by bovine conglutinin, indicating that the classical activation pathway was involved.