Growth inhibition of marek's disease T‐lymphoblastoid cell lines by chicken bone‐marrow‐derived macrophages activated in vitro

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Abstract
Studies have been performed on the induction of cytostatic activity of cultured chicken bone‐marrow‐derived macrophages. Cultured macrophages were exposed to supernatants of ConA‐stimulated spleen cell cultures (lymphokines), lipopolysaccharide (LPS), ConA or infectious bursal disease virus (IBDV). Cytostatic activity of macrophages was examined by testing their growth‐inhibiting effect on T‐lymphoblastoid Marek's disease cell lines RP‐1, HP‐2 and MSB‐1 as target cells. Lymphokines, LPS and IBDV caused considerable enlargement of adherent macrophages. Results of cytostasis assays suggested that morphological signs of macrophage activation were not correlated with the cytostatic potency of activated macrophages. Lymphokine‐activated macrophages caused at least an 80% growth inhibition of target cells, whereas LPS, ConA or IBDV‐activated macrophages exhibited only a marginal cytostatic effect in the range of 20%. Attempts to detect soluble cytostatic factors in supernatants of activated macrophage cultures failed or had equivocal results. Untreated macrophages were rarely cytostatic at an effector:target cell ratio of I:1 to 4:1, and they stimulated RP‐1 cell growth if these cells were seeded at suboptimal concentrations. The results suggest that the suppressor activity of macrophages from Marek's disease virus‐infected chickens, as demonstrated by other authors in vitro, is probably a result of nonspecific immunomodulation in vivo where lymphokines may also play a major role.