Increased adjuvant efficacy in stimulation of antibody responses after macrophage elimination in vivo

To investigate whether macrophages influence the efficacy of adjuvants, we locally eliminated lymph node macrophages with dichloromethylene diphosphonate containing-liposomes before primary immunization. After macrophage elimination, animals were immunized with a soluble antigen (TNP-KLH; 2,4,6-trinitrophenyl-keyhole limpet haemocyanin) either in phosphate-buffered saline (PBS), in complete Freund's adjuvant (CFA), or in Specol. Specol is a water-in-oil emulsion, considered to be less aggressive than CFA, but equally effective. A secondary immunization followed with TNP-KLH. In vivo macrophage elimination before Specol/TNP-KLH immunization resulted in increased adjuvant efficacy as measured by (primary) antibody responses. This suggests that the activity of Specol is not primarily mediated through macrophages but rather through other antigen-presenting cell types (e.g. dendritic cells, B cells, fibroblasts). The overall quality of produced antibodies, in terms of isotype distribution and affinity maturation, remained the same. After primary injection, CFA/TNP-KLH immunization resulted in significantly higher antibody responses in macrophage-depleted animals and antibody responses did not increase significantly after secondary immunization. However, a booster effect was found when macrophages were not eliminated before CFA/TNP-KLH immunization, suggesting that the presence of macrophages during the first weeks of the primary immune response is essential for the induction of an effective secondary response in CFA immunizations. In conclusion, macrophage depletion before immunization with a soluble T-cell-dependent antigen combined with Specol may enhance specific antibody responses without changing the isotype or affinity of the antibodies.