Nippostrongylus brasiliensis: Mast cells and histamine levels in tissues of infected and normal rats

Mast cell numbers and histamine concentrations were determined in the jejunum, mesenteric lymph node (MLN), thymus and trachea of normal (sham) Lewis male rats and in those infected with 3000 larvae of the intestinal nematode, Nippostrongylus brasiliensis. Changes in the wet weights of the MLN and thymus following infection were documented also. In infected rats the jejunal mast cells disappeared initially but increased dramatically between Days 15 and 19 to levels about 20 times normal. Jejunal histamine, as assayed by the enzymatic-isotopic assay, paralleled the mast cell hyperplasia. Mast cell changes in the trachea were clear and tracheal histamine levels did not change significantly following injection. Near the time of worm expulsion thymic atrophy was evident but thymic weight recovered subsequently. Mast cell numbers did not appear to change in the thymus but, correlated with the atrophy, the histamine content (μg/g) increased significantly. The MLN increased in weight five fold after infection and mast cell hyperplasia occurred in the node. Following an initial decrease in histamine in the MLN, significant elevation correlated with the mast cell hyperplasia. N. brasiliensis infection of rats provides a system to study the mechanisms of mast cell hyperplasia and the role of histamine in immune responses.