Antigen endocytosis and presentation mediated by human membrane IgG1 in the absence of the Ig alpha/Ig beta dimer

Membrane immunoglobulin (mIg) M and D heavy chains possess minimal (KVK) cytoplasmic tails and associate with the Ig alpha/Ig beta (CD79) dimer to achieve surface expression and antigen presentation function. In contrast, the cytoplasmic tail of mIgG is extended by 25 residues (gamma ct), We have tested the possibility that mIgG can perform antigen capture and presentation functions independently of the Ig alpha/beta dimer. We show that CD4/gamma ct chimeras are efficiently endocytosed partially dependent on a tyrosine residue in yet. In addition, human mIgG was expressed on the surface of Ig alpha/Ig beta-negative non-lymphoid cells and mediated antigen capture and endocytosis. Antigen-specific human mIgG targeted antigen to MIIC-type vesicles in the Ig alpha/beta negative melanoma Mel JuSo and augmented antigen presentation 1000-fold, identical to the augmentation seen in Ig alpha/beta-positive B-cells expressing the same transfected mIgG. Thus, unlike mIgM, mIgG has autonomous antigen capture and presentation capacity, which may have evolved to reduce or eliminate the BCR's dependence on additional accessory molecules.