Aging-induced changes in 24-h rhythms of mitogenic responses, lymphocyte subset populations and neurotransmitter and amino acid content in rat submaxillary lymph nodes during Freund's adjuvant arthritis

In young (two months) and aged (18 months) male rats injected s.c. with Fre und's adjuvant or adjuvant's vehicle 18 days earlier, 24-h variations in mi togenic responses, lymphocyte subsets and monoamine and amino acid content were examined in submaxillary lymph nodes. Mitogenic responses to concanava lin A (Con A) and lipopolysaccharide (LPS) were higher during the light pha se of daily photoperiod. Old rats exhibited a suppressed or impaired mitoge nic response to Con A but not to LPS. Acrophases of 24-h rhythm in lymphocy te subset populations in submaxillary lymph nodes were: 18:37-19:44 h (B ce lls), 09:00-10:08 h (T and CD4(+) cells) and 12:19-15:58 h (CD8(+) cells). Aging augmented B cells and decreased T, CD4(+) and CD8(+) cells. Significa nt correlations were found between Con A activity and T cells, between lymp h node 5HT content and B, T and CD8(+) lymphocytes, and between lymph node 5HT and taurine and GABA content. Aging increased lymph node 5HT content bu t did not modify NE content. Lymph node concentration of aspartate, glutama te and taurine was higher at night while that of GABA attained peak values at late afternoon. Old rats injected with Freund's adjuvant showed a higher mean value (glutamate) and smaller amplitude (glutamate, taurine) than the ir respective young controls. The results further document the effects of a ging on the chronobiology of the immune system. (C) 2001 Elsevier Science I nc. All rights reserved.