Influence of suspension on the expression of protective immunological memory to murine Listeria monocytogenes infection

Female BDF1 mice were immunized with virulent Listeria monocytogenes, which resulted in the generation of a long-lived state of protective immunological memory for this facultative intracellular bacterial pathogen. The influence of antiorthostatic suspension, a ground-based model employed to simulate certain aspects of weightlessness that occur during spaceflight, on the capacity of these mice to express memory immunity was evaluated. Memory-immune mice were suspended by the tail in the orthostatic or antiorthostatic position and were reinfected with a lethal dose of virulent L. monocytogenes. It was found that suspension did not influence the kinetics of bacterial growth in vivo when the rechallenge infection was started concurrently with the suspension. However, mice that were reinfected on day 2 or 4 of the suspension exhibited an enhanced capacity to eliminate the infection. Attenuation of this enhancing effect was observed when mice were infected on day 7 of the suspension. These results indicate that the stress of antiorthostatic suspension can influence the capacity of the murine host to express protective immunological memory to pathogenic bacteria.