Soluble factors in immune sera of mice. I. Specific and non-specific suppressive activity.

Serum collected from mice 7 days following immunization with heterologous erythrocytes (SRBC, HoRBC) contained potent and specific immunosuppressive activity. When the serum was filtered through a Diaflo UM-10 membrane the activity was recovered in the filtrate, indicating that a factor less than 10,000 Daltons is responsible for it. Filtrates obtained from animals immunized with soluble antigens (BSA, POL) in FCA suppressed the 7S response to SRBC but had no effect on the 19S response. This non-specific suppressive effect on the7S response was also shown by filtrates obtained from sera of animals injected with FCA or other adjuvants (LPS, poly A:U). The 19S response to SRBC was either not affectd (LPS, poly A:U) or actually enhanced. (FCA). The SRBC-induced filtrates markedly suppressed the espression of DH to SRBC.