Binding of antibodies raised against tumour necrosis factor alpha (TNF alpha) to blood vessels and macrophages in inflamed synovial tissue.

The distribution of tumour necrosis factor alpha (TNF alpha) in rheumatoid synovium has been investigated. Ten rheumatoid synovia were compared with seven normal synovia and a range of other tissues, using one polyclonal and six monoclonal antibodies. A common staining pattern was obtained with five reagents. Absence of staining of tissue with the other reagents may relate to binding to different epitopes. Excluding cross-reactivity with smooth muscle seen with two reagents, results with the first five reagents were as follows. Normal tissues showed either no staining or faint staining of venular endothelium. In addition skin keratinocytes and colonic mucus showed staining. Rheumatoid synovium showed staining of venules and weaker staining of mononuclear cells, both as individual cells in the deep tissue and more uniformly in areas of the lining layer. The majority of cells that stained for TNF alpha double-stained for CD68 (macrophages). These represented less than 10% of CD68-positive cells. Isolated cells staining for TNF alpha stained for CD3 (T-cells), forming less than 1% of the total T-cells. The presence of staining of venular endothelium suggests that the cytokine may be synthesised by endothelial cells or may be taken up after production by macrophages.