Dendritic Leucocytes Pulsed with Monoclonal Antibody-hapten Conjugates Elicit Vigorous Primary Humoral Responses in Vivo

Purified dendritic leucocytes (DL) were pulsed briefly in vitro with haptenated monoclonal antibodies (MoAb) to MHC class II and immediately injected i.v. into syngeneic recipients. Strong anti-hapten humoral responses were observed even though only a few picomoles of specific MoAb-hapten conjugates were injected with the DL. In contrast, DL pulsed with control conjugates, i.e. haptenated non-binding MoAbs, gave only weak responses. DL thus, can take up, process and present protein antigens even after brief exposure in vitro, and their immunogenicity is enhanced by pulsing with antigen conjugated to specific MoAbs. Furthermore, in the presence of fetal calf serum (FCS), but not normal rat serum, the control MoAb W6/32 (against human MHC class I) bound to DL. The vigorous primary humoral response achieved following this pulsing indicates that it is the binding and the corresponding increased uptake that enhances the immunogenicity of the DL.