Bovine monocytoid cells transformed to proliferate cease to exhibit lineage-specific functions

Bovine cell lines of the monocyte-Mphi lineage were tested for surface marker expression and were characterized with respect to functions. Cell lines tested encompassed an SV40-transformed cell line (Bo-Mac), a spontaneously emerging monocytoid cell line (M617), and T. annulata-transformed lines derived from bovine Mphi. All lines failed to express surface markers expressed by 1 degrees Mphi, with the exception of CD44, WC9 and the DH59 myleoid cell marker. T. annulata-derived lines expressed, in addition, CD45 and MHC-class-II molecules. Except for nonspecific esterase staining, none of the typical macrophage functions were expressed by any of the cell lines. These included phagocytosis of opsonized E. coli bacteria and of IgG-treated erythrocytes, eliciting of an oxidative burst, the ability to express type-I-interferon (IFN) and to respond to lipopolysaccharide, as determined by four different effector functions (nitric oxide synthesis, tumor necrosis factor (TNF) secretion, IFN production and procoagulant activity upregulation). When transformation induced by T. annulata was reversed by chemical elimination of the parasite, cells ceased to proliferate but started to acquire some of the phenotypic characteristics of Mphi. This suggests that regardless of their origin, exponentially growing bovine cells of the monocyte-Mphi lineage poorly represent a lineage-specific phenotype and should be used with caution in immunological studies.