Individual differences in susceptibility to infection have been of a subject of interest for decades. This variation can come from different settings of exposure or constitutional make-up of the hosts. Here I show two study results on two infectious diseases, namely, tuberculosis and HIV-1 infection.
　　Latent TB infection (LTBI) is a consequence following contact with people with active TB. To predict who will develop LTBI, we proposed a 8-point scoring system using data routinely available during contact investigation. This scoring system was developed, including reaction to tuberculin skin test of the contacts, as well as smear-positivity, residence in high-incidence areas, and sex of the index cases. The risk of developing active TB within 3 years is 100, 7.8, 4.3, 1.0, 0.7, and 0.2% for contacts with risk scores of 7, 6, 5, 4, 3, and 2, respectively. Hence, the setting of contact is crucial for LTBI infection.
　　HIV-1 infection is one model to examine the role of cellular protein in regards to susceptibility to infection. A cellular protein, MRJ-L, that associates with HIV-1 Vpr protein plays a crucial role in determining the fate of infection. We found that expression of MRJ-L in monocyte-derived macrophages was significantly higher in HIV-infected individuals (n=31) than their uninfected counterparts (n=27). Among prospectively followed, male homosexual subjects, 20/50 developed HIV-1 infection. Bayesian multiple logistic regression revealed that playing a receptive role and levels of MRJ-L in macrophages were two risk factors for HIV-1 infection. Ex vivo cellular experiments revealed that MRJ-L facilitated Vpr-dependent nuclear localization of virus.
　　In summary, exposure scenario and expression patterns of pathogen-interacting cellular factors are two important factors to determine the fate of an infection. Better understanding of these will guide the development of more effective strategy to combat infectious diseases.