MATURATION OF THE MITOGEN RESPONSIVENESS, AND IL2 AND IL6 PRODUCTION BY NEONATAL SWINE LEUKOCYTES

The maturation of the immune system of neonatal piglets was studied by following changes in the phenotypic composition and function of blood -borne leukocytes. The proportion of mature T and B lymphocytes decrea sed in the first week of birth and the circulating cells had poorly de veloped capacities to respond to mitogens and to secrete interleukins. From the end of the first week, however, there was a steady increase in the proportion of mature T cells (CD4+ and CD8+) and B cells in blo od until 6-7 weeks after birth, when the study was ended. By 3-4 weeks , the relative proportions of different lymphocyte subsets resembled a n adult-type composition. As they increased in prevalence, lymphocytes also developed capacities to proliferate and secrete interleukins. Pr oliferative responses to T-cell and B-cell mitogens reached adult leve ls within 2 weeks and 4-5 weeks, respectively. Blood leukocytes produc ed large quantities of IL6 by 1-2 weeks after birth and IL2 by 2-3 wee ks. In contrast to lymphocyte patterns, the myeloid and granulocyte li neages were dominant at birth but then declined steadily. Unlike lymph ocytes, the monocytes, macrophages and granulocytes appeared to be ful ly functional from the time of birth and exhibited a strong oxidative burst after appropriate stimulations. The magnitude of this response r emained constant over the first 6-7 weeks. These results indicate that the first 3-4 weeks of post-natal life are a particularly susceptible interval for newborn piglets because constitutive and functional comp onents necessary for specific cellular immune responses remain immatur e. This deficit may be offset by non-specific cellular mechanisms and maternally derived antibodies. (C) 1997 Published by Elsevier Science B.V.