This family consists of several invasion associated locus B (IalB) proteins and related sequences. IalB is known to be a major virulence factor in Bartonella bacilliformis where it was shown to have a direct role in human erythrocyte parasitism. IalB is upregulated in response to environmental cues signaling vector-to-host transmission. Such environmental cues would include, but not be limited to, temperature, pH, oxidative stress, and haemin limitation. It is also thought that IalB would aide B. bacilliformis survival under stress-inducing environmental conditions. The role of this protein in other bacterial species is unknown.