Evaluation of relation between mutant VirB2 virulence factor in Brucella melitensis with immunogenicity and intracellular survival

ABSTRACT

The Brucella melitensis virB operon, encoding a type IV secretion system [T4SS], is required for intracellular replication and persistent infection in the mouse model. The product of the second gene of the virB operon, virB2, is predicted to be localized at the bacterial surface, where they could potentially interact with host cells. Studies to date have focused on characterization of transposon mutations in this gene, which is expected to exert polar effects on downstream genes. We researched on the evaluation of relation between virB2 mutant with immunogenicity in mouse model and intracellular replication in macrophages J774. In order to determine whether VirB2 is required for the function of the T4SS apparatus, we constructed and characterized deletion mutation of virB2 and kanamycin resistance gene replaced instead of virB2. For demonstration of intracellular replication, macrophages J774 and BALB/c mices were infected with wild type Brucella melitensis and mutated. After 48 h, number of mutated Brucella severe decreased severly compaired to wild type in macrophages J774, and Brucella with virB2 deletion decreased from 1x10[6] CFU/spleen less than 1000 CFU/spleen during 8 weeks, also total IgG increased in both but IL-12 and IFN-gamma increased only in wild type. VirB2 was essential for intracellular replication in mouse models and J774 macrophages. The virB2 mutant was unable to cause persistent infection in the mouse model, demonstrating the essential role of VirB2 in the function of the T4SS apparatus during infection and secreting IL-12 and IFN-gamma, but VirB2 dispensable for secretion of total IgG