Expression of tumor necrosis factor-alpha receptors on bovine macrophages, lymphocytes and polymorphonuclear leukocytes, internalization of receptor-bound ligand, and some functional effects.

Tumor necrosis factor-alpha (TNF) is a pluripotent protein produced by cells of the monocyte-macrophage lineage. It has important pro-inflammatory functions and is thought to be involved in the pathogenesis of viral-bacterial lung infections of cattle. Binding and internalization of gold-labeled TNF (TNF-G10) by bovine alveolar macrophages as well as by peripheral blood mononuclear leukocytes (PBML) and polymorphonuclear granulocytes (PMN) have therefore been investigated in conjunction with studies of the effect of TNF on some leukocyte functions. TNF-G10 bound to all leukocyte types to varying extents, which however, did not correlate with the influence of TNF on cell functions. Thus, PMN appeared to possess the lowest number of TNF-receptors, but were nevertheless the most sensitive to functional modulation by TNF. The expression of TNF-receptors appeared to be regulated by other cytokines such as IFN-gamma and IL-2, with IFN-gamma down-regulating receptor expression on all cell types, and IL-2 up-regulating receptor expression on lymphocytes. In macrophages internalization of TNF-G10 occurred via clathrin-coated structures, whereas in lymphocytes and PMN the endosomes appeared to lack distinct coating.