Antigen processing in earthworms

The administration of protein antigens into earthworms Lumbricus terrestris and Eisenia foetida induces the formation of antigen-binding protein (ABP) with the maximum response occurring between days 4 and 8. High proteolytic activities observed both in coelomocytes and in coelomic fluids cause rapid antigen degradation; the majority of antigen is digested during the first 24 h. To analyze the role of proteolytic processing of antigen in ABP response in vitro, the intact antigen (ARS-HSA) as well as its proteolytic fragments were added to tissue explant cultures and ABP formation followed by indirect ELISA using mAb to ABP. The response to small fragments was comparable to that induced by intact ARS-HSA. Furthermore, the response to intact antigen was almost completely blocked by the non-toxic serine protease inhibitor Pefabloc, while the response to small fragments was only slightly reduced. The kinetics of response to intact antigen significantly differed from that induced by small (< 3 kDa) fragments. We suggest that proteolytic processing is involved in the stimulation of ABP formation.