HSP Roles as Biomarkers and Antigens in Bacterial and Viral Infections

Both prokaryotes and eukaryotes tolerate different stress conditions (e.g., metabolic, environmental and pathophysiological stress) by up-regulating the expression of heat shock proteins (HSPs). These proteins are divided into six main families such as Hsp100, Hsp90, Hsp70, Hsp60, Hsp40 and small heat shock proteins (sHsps) based on their molecular weights (MW) and sequence homology [1, 2]. Among them, sHsps (MW: 12-43 kDa) including Hsp27, αAand αB-crystallin are distinguished by the presence of a highly conserved sequence (80-100 amino acids) called as the “α-crystallin domain” (ACD) [3-5]. The studies showed that Hsps are targets of the host immune responses (e.g., Hsp60 in bacterial infections) [6] and play a significant role as a biomarker in infectious diseases. For example, women with pre-existing antibody responses to chlamydial Hsp60 (CHsp60) indicated a high risk of developing pelvic inflammatory disease (PID) during a new chlamydial infection as compared to women without CHsp60 antibody [7]. Hsps can elicit strong humoral and cellular immune responses in various infectious diseases [8], [9]. For instance, antibody and T cell responses specific for Hsp60 were induced in leprosy and tuberculosis (TB) patients as well as in individuals vaccinated with Mycobacterium bovis BCG [8, 10-12]. In contrast, Hsp70 has an important role in viral infections such as rabies virus infection [13].