Phenotypic changes in mast cells proliferating in the rat lung following infection withNippostrongylus brasiliensis

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Abstract
Numerous mast cells appear in rat pulmonary granulomas associated with infection by the nematodeNippostrongylus brasiliensis. The kinetics and histochemical characteristics of these mast cells were studied and compared with those of intestinal mucosal mast cells. The number of lung mast cells showed a distinct increase 2 weeks after infection and then gradually decreased. In a study using bromodeoxyuridine (BrdU), which is incorporated into cellular DNA at the S-phase, mast-cell labeling was highest 12–13 days after infection, and returned to the normal level 21 days after infection. This indicates that lung mast cells proliferate for only a short time. Intestinal mucosal mast cells showed a similar pattern. A parallel increase in globule leukocytes in the bronchus and trachea was also observed. The proliferating lung mast cells in the early period were stained with alcian blue but were negative for berberine and avidin-biotin-peroxidase complexes (ABC). In a lung extract, type II protease, which has been reported to be confined to mucosal mast cells, increased until the 14th day, and decreased thereafter. This indicates that lung mast cells, at least in the initial stage of proliferation, are similar to intestinal mucosal mast cells in terms of their cell kinetics and histochemical characteristics. However, histochemical studies of mast cells at a later stage of infection showed a different result. After 12 weeks of infection when the mast-cell density was still high, almost all the lung mast cells became positive with berberine and/or ABC, both of which are supposed to be bound to heparin within mast cell granules. The latter result shows that after a long period of infection, lung mast cells resemble connective tissue mast cells. Thus, a phenotypic change in mast cells from the mucosal to the connective tissue type may have occurred.

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