Nonspecific early protective immunity in Francisella and Listeria infections can be dependent on lymphocytes.

Normal mice, but not lymphocyte-deficient or B-cell-deficient mice, given a sublethal infection of Francisella tularensis LVS survive a secondary lethal challenge of more than 10,000 50% lethal doses given 3 days later. In this work, we show that similar early protection that is also strongly lymphocyte dependent operates in Listeria monocytogenes infection. Since sublethal infection with either LVS or L. monocytogenes protects against heterologous lethal challenge, this early protection is nonspecific.