Sendai virus infection of normal and protein malnourished mice: response of airway leukocytes to infection

We examined the cells recovered by bronchoalveolar lavage (BAL) during the course of respiratory infection caused by Sendai virus in normal (20% protein diet) and malnourished (2% protein diet) mice. As in our previous experiments, mortality in normal mice was 32% in comparison with 87% in the malnourished group. Virus was isolated until the 5th day in normally fed mice and until the 9th day in the malnourished group. BAL fluids contained 97% macrophages before infection in both groups. During infection there was a progressive lymphocyte response, reaching a peak of 60-70% on day 5 in the normal mice and on days 7-9 in the malnourished group. Subtyping of BAL cells by flow cytometry indicated that in uninfected animals lymphocytes were largely CD4-bearing. On days 3 and 5 post-infection most mononuclear cells were Thy 1.2-positive, but lacked both CD4 and CD8 markers and were therefore probably natural killer cells. Beginning on day 5, in both diet groups CD8-positive cells rose to become the predominant subset. In the 20% protein diet group, CD8-positive cells reached a maximum of 60% on day 7, whereas in the 2% protein diet group this level was not reached until day 9. These results were consistent in three separate experiments. In malnourished mice the delayed appearance of CD8-bearing cells in the airway may contribute to the higher mortality and delayed virus clearance during Sendai virus infection.