CD4 and infection: Immunization of C3H/HeN mice with these peptides either alone, pooled, or expressed as a recombinant fusion protein resulted in enhanced expression of IFNγ and TNFα by CD4+ T cells as well as increased immunoglobulin G1 (IgG1) and IgG2a production in the infection with R. rickettsii. Furthermore, immunization with the pooled peptides led to reduced bacterial burden [199].