The immune response in lymphoid organs of rat: A cytochemical study

Variations in the activity of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), dihydrofolate reductase (DHFR) and alkaline phosphatase (ALP) were studied, using the light microscope (LM), and cytochemical reactions in lymphoid organs (lymph node, spleen, thymus) of rats, up to day 5 following Escherichia coli immunisation. Increased levels of LDH and DHFR in the T-area of lymph nodes and of spleen were seen from day 2 to day 4 postimmunisation. The SDH reaction in lymph nodes and in the spleen increased during days 2 and 3 but decreased on day 4 postimmunisation. Considerable increases in the activities of LDH and SDH were seen in thymus at all times postimmunisation. The DHFR reaction product also increased but less markedly. No reaction for ALP was observed in lymphocytes of lymphoid organs studied. Following E. coli immunisation, there is an increase in glycolytic and respiratory metabolism, and in the synthesis of proteins in T-dependent areas of lymphoid organs. These increases are correlated with immune activation of T-cells in these organs.