The properties of the mononuclear phagocyte (Mph) high-affinity Fc receptor, FcRI, were investigated using a novel monoclonal antibody (mAb) designated 10.1. This receptor was shown to be a protein of 71 kDa, presented chiefly on monocytes and the myeloid cell lines U937 and HL60. mAb 10.1 inhibited the binding to Mph of erythrocytes opsonized with rabbit IgG or human IgG3. It also blocked T cell proliferation induced by murine CD3 mAb of the IgG2a but not the IgG1 subclass. These results suggest that rabbit IgG, human IgG3 and murine IgG2a all bind to FcRI in a similar manner and that mAb 10.1 reacts with an epitope on FcRI near to the binding site for the Fc region of IgG. In addition, although it is well known that FcRI has a high affinity for both monomeric human IgG1 and IgG3, we show in this study that while erythrocytes opsonized with human IgG3 bind to Mph, equivalent cells opsonized with IgG1 surprisingly do not. These results define further the nature of the constraints on the interaction between Mph FcRI and particular IgGs.

A new monoclonal antibody (mAb), named 3.9, is described that is specific for the p150,95 molecule, a member of the LFA-1, CR3, p150,95 family of human leukocyte differentiation antigens. The LFA-1 molecule participates in a variety of T cell interactions and the CR3 molecule is the receptor for the complement component iC3b, but little is known about the p150,95 molecule. Here we show that the expression of p150,95 is confined to myeloid cells. mAb 3.9 reacts variably with neutrophils, more strongly with monocytes and is most strongly expressed on tissue macrophages. Using this mAb and others, we have examined the heterogeneity of tissue macrophages. Cells such as Langerhans' cells, dendritic reticulum cells and osteoclasts failed to react with these mAb and thus, probably do not belong to the mononuclear phagocyte lineage. Using a new double-labeling technique, we investigated lymphoid tissue for dendritic cells bearing class II molecules which might function in interactions with T cells. In T cell areas macrophages expressing class II markers were seen but there was no evidence for other types of dendritic or interdigitating cells which expressed class II molecules but not macrophage epitopes. The conclusion from this survey was that the most prominent cell with dendritic morphology found in the T cell areas of lymphoid tissue was a macrophage.

No abstract

No abstract