Peripheral blood and synovial fluid monocyte activation in inflammatory arthritis. I. A cytofluorographic study of monocyte differentiation antigens and class II antigens and their regulation by gamma-interferon.

Recent study of the expression of monocyte differentiation antigens (MAg) and HLA-DR on peripheral blood monocytes (PBM) has led to the recognition of resting and activated monocyte phenotypes. The former is identified by the expression of large amounts of MAg (i.e., Mo2 and 63D3) and small amounts of HLA-DR, while the latter is identified by the reverse. We studied the phenotypes of PBM and synovial fluid monocytes (SFM) of patients with chronic inflammatory arthritis and found that PBM were primarily resting and SFM were usually activated. In addition, we measured the degree of modulation of MAg and HLA-DR by gamma-interferon (gamma-IFN). Patient PBM reacted the same as PBM from normal individuals (i.e., MAg decreased and HLA-DR increased after exposure to gamma-IFN). However, in patient SFM, HLA-DR did not increase with exposure to gamma-IFN because expression was already maximal. Interestingly, MAg could still be down-regulated on gamma-IFN-treated SFM, even when expression began at a very low level (i.e., activated phenotype). This independent regulation of MAg and HLA-DR suggests that macrophage activating factors other than gamma-IFN may be responsible, in part, for the activated phenotypes observed.