The immunogenic capacity of antigen taken up by peritoneal exudate cells.

The immunogenic capacity of protein antigens has been compared for the free and peritoneal exudate cell (PEC)-bound forms. The response of CBA mice to BSA provides the reference system, but lysozyme, ovalbumin, HSA and modified BSA were also studied. Uptake is approximately equally efficient and . PEC-bound antigen, estimated by radioactivity is far more potent than the free form in inducing primary immunization. The following properties were also found: (i) viable PEC are required; (ii) irradiation of the cell donor 2–7 days before giving antigen inhibits immunization, but irradiation after uptake does not do so; (iii) mice are susceptible to immunization during their phase of recovery from paralysis; (iv) PEC do not retain large amounts of antigen for long; (v) the activity does not depend solely on a minor, phagocytosisprone fraction of the antigen; (vi) allogeneic transfer of PEC reduces their immunogenic capacity; (vii) paralysed hosts are not susceptible to immunization, but PEC from paralysed donors are effective; and (viii) the enhancement of immunogenic capacity does not apply to the secondary response. The conclusion may be drawn that the retention of small quantities of antigen by macrophages plays an essential role in some, but probably not all types of immune response.