Cross-linking of neutrophil CD11b results in rapid cell surface expression of molecules required for antigen presentation and T-cell activation.

Recent studies suggest that neutrophils may play a role in antigen presentation. In support of this hypothesis it has been shown that these cells appear to contain cytoplasmic stores of molecules required for this function, i.e. major histocompatibility complex class II (DR) antigen, CD80 and CD86. In this study we have considered a mechanism for the translocation of these preformed molecules onto the cell surface which does not require active synthesis. Cross-linking of the Mac-1 molecule (CD18 + CD11b) was shown to result in rapid cell surface expression of CD80, CD86 and DR antigen on the surface of normal human peripheral blood neutrophils. A distinct subpopulation (approximately 20%) of neutrophils appeared to be enlarged and were found to express significantly elevated levels of these molecules on the cell surface following cross-linking of CD11b when compared with control cells. The level of expression of CD80, CD86 and DR antigen on these large cells was comparable to, and in some cases greater than, the levels found expressed on the surface of monocytes obtained from the same donors. In addition, these cytoplasmic molecules were shown by confocal laser microscopy and by immunoelectron microscopy to be located within secretory vesicles. Following rapid translocation onto the cell surface, CD80 and CD86 appeared to be colocalized within large clusters reminiscent of the supramolecular antigen clusters previously found on conventional antigen-presenting cells. These findings therefore lend further support for the hypothesis that neutrophils may have a role to play in antigen presentation and/or T-cell activation.