COMPARATIVE IN-VITRO PHAGOCYTOSIS AND F-ACTIN POLYMERIZATION OF BOVINE NEONATAL NEUTROPHILS

Analysis of neonatal neutrophil (PMN) functions should help to reveal factors which could contribute to the impaired host defense system of neonates. We analysed functional parameters of PMN from newborn calves (N-PMN) and adult bovines (A-PMN): cellular volume and F-actin conten t upon stimulation with complement factors, by cytofluorometry and pha gocytosis of E. coli 78:80B with a colorimetric assay. Polymerization of F-actin was rapid in both N- and A-PMN, but reached higher levels i n N-PMN. N-PMN are significantly smaller than A-PMN throughout the who le activation time. Percentage of phagocytosing PMN, the rate of phago cytosis, and the rate of killing are similar between A- and N-PMN afte r opsonization of bacteria with adult serum (AS). Opsonization with ne wborn serum (NS) reduced all three examined parameters: in A-PMN more (P < 0.001) than in N-PMN (P < 0.05). However, when phagocytosis was c ompared following age-matched opsonization (N-PMN and NS; A-PMN and AS ), N-PMN phagocytosed less (P < 0.001) bacteria per PMN than A-PMN. Ad ditionally, steroidal (dexamethasone) and non-steroidal (phenylbutazon e) anti-inflammatory drugs inhibited phagocytosis by N-PMN less than b y A-PMN. Higher relative F-actin content of N-PMN can be correlated wi th the documented functional hyperactivity of bovine N-PMN. However, t he exaggerated impairment of phagocytosis in calves observed after age -matched opsonization of bacteria could potentially indicate a specifi c host defence defect.