Target-cell susceptibility and lung phagocyte activity in mice with influenza virus resistance lowered by glucocorticoidal immunosuppression

The results of the study showed that subcutaneous kenalog (Kn) lowered the resistance of mice to influenza virus (InV), as was seen by a decrease in 50% lethal dose and an increase in the degree of pulmonary tissue lesion, and the susceptibility of the lungs to InV, seen by the fact that 50% aerogenic infective dose (AID50) was significantly higher in the main group (Kn+InV) than in controls, which received Hanks solution subcutaneously (HS+InV). In vitro, 50% infective doses of InV for suspension of pulmonary and tracheal cells, characterizing their susceptibility to InV, were similar in Kn mice and controls. At the same time, lower resistance and higher degree of pulmonary inflammation noted in Kn mice after receiving a dose of InV that was much higher than an infecting one, was accompanied by the prevalence in the number as well as phagocyte and superoxide-producing activity of neutrophiles (Nph) over the same parameters for alveolar macrophages (AMph) as early as two days after receiving InV dose, vs. InV-infected controls. Evidently, one of the reasons for lower resistance to InV after Kn administration is significant disbalance between the functional activity of AMph and Nph populations. Ineffective AMph clearance of the lungs from InV and excessive number of recruited Nph and products of tissue disintegration may favor the development of respiratory failure and infectious-toxic shock, which leads to lower resistance in animals which receive Kn before InV infection.