Bronchoalveolar Leucocyte Responses to Trickle Infections with Nippostrongylus brasiliensis in Rats

Abstract

There is a need for experimental systems allowing study of host responses generated by continuous, low-level exposures to parasites. To assess the pulmonary inflammatory responses in different types of exposure to infection we used bronchoalveolar lavage (BAL). Rats sensitized by 500 Nippostrongylus brasiliensis larvae given in 20 doses over a 4-wk period (group T) and challenged with 500 larvae 33 days after the initial exposure were compared to rats initially given 1 sensitizing dose of 500 larvae (group B) and also to naive, sham-treated (group S) rats, subsequently challenged with 500 larvae. BAL performed prior to final challenge revealed markedly increased numbers of macrophages and eosinophils in group T, but there were only minor changes in numbers of these cells in group B. After final challenge, numbers of BAL macrophages and eosinophils were greater in group T than in group B, although in group B there was a rapid increase in numbers of these cells. Changes in numbers of BAL neutrophils were not correlated with previous sensitization to N. brasiliensis. Thus, there was a pronounced influx of leucocytes into the pulmonary lumen after secondary challenge in rats sensitized by repeated exposures to low doses of larvae.