Lack of Anti-macrophage Species Specificity in Anti-lymphocytic Serum

Abstract

THE mode of action of anti-lymphocytic serum (ALS) in suppressing cellular and humoral immune responses remains uncertain^1,2 although there is evidence that it acts preferentially on a sub-population of thymus derived small lymphocytes^3–5. Its action, however, is not confined to lymphocytes but it also affects neutrophils⁶, epithelial cells⁷, and macrophages^8–14. On the other hand, specific anti-macrophagic activity of ALS has been either questioned¹⁵ or refuted^16–18. Anti-neutrophil activity of ALS may be responsible for the anti-inflammatory properties of ALS¹⁹ which have been shown to be separate from its immuno-suppressive activity and not to prolong graft survival²⁰. Macrophages and monocytes, however, play an important role in the immune response²¹ and anti-macro phage activity might account for much of the immuno-suppressive capacity of ALS. Previous reports indicated that ALS was species but not strain specific with respect to both anti-lymphocytic⁸ and anti-macrophagic activity¹³. Species specificity of anti-lymphocytic activity is, however, not absolute^22,33,34; and this report demonstrates that the same is true for anti-macrophage activity, particularly between related species.