945 ONTOGENY OF PHAGOCYTE MOVEMENT IN THE OVINE

Abstract

Movement of phagocytic cells constitutes a major host defense mechanism. Previous studies from this and other laboratories have demonstrated diminished movement of neonatal PMNs and MNLs. Nothing, however, is known of the ontogeny of PMN and MNL movement. We now report such studies in the ovine. Fetuses ranging in age from 120 to 150 days (term) were delivered of date bred ewes by Caesarean section. PMNs were obtained from venous blood and chemotaxis was measured by a modified Boyden technique, utilizing 3μ cellulose acetate filters. Endotoxin activated pooled normal sheep plasma was the chemoattractant. Pulmonary alveolar macrophages (PAM) were obtained from the first 10-12 cc of tracheobronchial aspirate. PAM were suspended in McCoy's medium to a final concentration of 1.5 × 10⁶/ml. Chemotaxis was studied by a modification of the method of Snyderman utilizing 8μ nuclepore filters. The data showed: 1) Regardless of age at delivery, PMNs and PAMs failed to show any chemotaxis. This correlated with marked neutropenia in the first blood sample obtained. Bone marrow examination, by contrast, showed normal granulocyte stores. Maternal ovine control PMNs and PAMs showed normal migration; 2) Following delivery, lamb PMNs developed chemotactic responses within several days. This correlated with rise in the peripheral neutrophil count to normal adult sheep levels. The absence of chemotactic response in utero was entirely unexpected and suggests a regulatory role on phagocyte function occurring during gestation and the birth process.

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