Lymphocytes Responding to Primary and Re-infection of Parainfluenza (Sendai) Virus in Mice

Abstract

The cells recovered in bronchoalveolar lavage (BAL) fluid after primary and re-infection of Sendai virus in mice w~re analyzed. In primary infection, total cell counts recovered in the BAL began to increase on day 5, reached a peak on day 7 of infection. One day after infection, there was a remarkable neutrophil response. Lymphocytes began to increase on the third day after infection, reaching a peak on day 5. Preinfection lymphocytes were largely CD4-bearing. Most of the lymphocytes on day 3 and day 5 were Thy 1.2-positive, but double negative for CD4 and CD8 which were thought to be natural killer cells. CD8 cells began to increase on day 5, reached a plateau of 60% since day 7, which coincided with disappearance of virus in the lung. Peripheral differential white cell counts showed a striking lymphopenia lasting 5 days, and CD4 bearing cells predominated throughout the post-infection period. After re-infection, lymphocyte response was more brisk, reaching a peak on day 3, but less prominent compared to that of primary infection. The most remarkable change was observed in the population of B-cells, reaching a plateau of 30% since day 3 after infection. In conclusion, there is a major influx of natural killer cells into the lung in the early phase, CD8 cells in the late phase of primary Sendai virus infection, and B-cells in re-infection. These changes are not reflected in the peripheral blood.