Increased T cell responses, owing to their memory of Lm antigens during the primary challenge, are responsible for enhanced protection during secondary Lm challenge.15 In Batf2−/− mice, a secondary Lm infection was more rapidly controlled with reduced bacterial burdens in the liver and spleen at 2 and 4 days after infection (Fig. S3N), suggesting that the absence of Batf2 might also enhance the ability of T cells to directly and/or indirectly control secondary Lm infection. This evidence concerns the gene BATF2 and infection.