Antigen targetting with monoclonal antibodies as vectors--II. Further evidence that conjugation of antigen to specific monoclonal antibodies enhances uptake by antigen presenting cells.

Immunization of rats with haptenized monoclonal antibodies (mAbs) against accessory cells enhances anti-hapten antibody responses. To see whether the mAb-conjugates really targetted the antigen (hapten) to the antigen presenting cells, we have investigated the lymph node distribution of locally injected radiolabelled conjugates. Compared with control conjugates, i.e. haptenized non-binding mAbs, a much larger proportion of the specific conjugates were retained in the draining lymph nodes. Whereas control conjugates were rapidly phagocytosed and degraded by macrophages, the specific conjugates were associated with the targetted accessory cells, which were radiolabelled for extended periods. Haptenated MRC OX6 (anti-MHC class II) gave strong labelling of interdigitating cells (IDC) in the paracortex with 70% of IDC still labelled by 4 days and 15% by 16 days following injection. By Western blots intact OX6 conjugates were still detected in the draining lymph node as long as 3 days after injections, whereas control conjugates were hardly detectable even by 24 h. The findings substantiate the idea that mAbs can be exploited for vectorial transport of antigens to accessory cells.