Chemotactic and phagocytic function of peripheral blood polymorphonuclear leucocytes in newborn foals

Chemotactic and phagocytic responsiveness of peripheral blood polymorphonuclear leucocytes (PMNLs) from 11 foals were analysed immediately after birth (pre-colostral) and at different times after colostrum ingestion. The number of foal PMNLs per microscopic field that had migrated through the filter in chemotaxis and the number of yeast particles ingested per foal PMNL in phagocytosis were significantly lower when tested with foal plasma before colostrum ingestion (chemotaxis, 2.0 +/- 0.55 (s.e.m.); phagocytosis, 0.98 +/- 0.352) than in tests 4 or more days after colostrum ingestion (chemotaxis, 17.6 +/- 3.88; phagocytosis, 3.87 +/- 0.410; P less than or equal to 0.005). A similar functional deficiency was found in foal PMNLs tested with pre-colostral foal plasma when compared to tests of the same cells with mare plasma (chemotaxis, 11.6 +/- 2.91; phagocytosis, 3.94 +/- 0.269; P less than or equal to 0.005). PMNLs from neonatal foals responded with normal functions to plasma from normal adult horses. Results of both assays suggest that pre-colostral foal PMNLs are functionally mature but the expression of their chemotactic and phagocytic functions depends on the humoral source of chemotactic and opsonic factors.