Effects of crowding of mice on humoral antibody formation and protection to lethal antigenic challenge.

The effects of grouping (crowding) on humoral antibody response to typhoid paratyphoid vaccine and subsequent protection from a minimal lethal challenge dose of Salmonella typhimurium were studied in white Swiss-Webster mice. The data show a trend between the degree of crowding and antibody response. Geometric mean titers of high density grouped mice were significantly lower than the geometric mean titers of the less crowded mice. Also, there were significantly less antibody responders in the high density grouped mice than in the less crowded mice. However, challenged with a minimal LD50 dose of Salmonella thphimurium, no deaths occurred in the immunized study group, regardless of measurable antibody level. In the nonimmunized controls, which were under the same stressor conditions, there was a significant difference between the level of crowding and death to challenge. The data show that nonimmunized mice in this study exhibited a marked increase in susceptibility to an infectious agent when under the stressor effect of crowding.