O-mannosylation of the Mycobacterium tuberculosis Adhesin Apa Is Crucial for T Cell Antigenicity during Infection but Is Expendable for Protection

Abstract

Glycosylation is the most abundant post-translational polypeptide chain modification in nature. Although carbohydrate modification of protein antigens from many microbial pathogens constitutes important components of B cell epitopes, the role in T cell immunity is not completely understood. Here, using ELISPOT and polychromatic flow cytometry, we show that O-mannosylation of the adhesin, Apa, of Mycobacterium tuberculosis (Mtb) is crucial for its T cell antigenicity in humans and mice after infection. However, subunit vaccination with both mannosylated and non-mannosylated Apa induced a comparable magnitude and quality of T cell response and imparted similar levels of protection against Mtb challenge in mice. Both forms equally improved waning BCG vaccine-induced protection in elderly mice after subunit boosting. Thus, O-mannosylation of Apa is required for antigenicity but appears to be dispensable for its immunogenicity and protective efficacy in mice. These results have implications for the development of subunit vaccines using post-translationally modified proteins such as glycoproteins against infectious diseases like tuberculosis.

Attrition of T-Cell Functions and Simultaneous Upregulation of Inhibitory Markers Correspond with the Waning of BCG-Induced Protection against Tuberculosis in Mice

“…at week 52 or thereafter. This viewpoint is further supported by a recent data from our laboratory, where boosting with Apa (Rv1860)-based subunit vaccine during the contraction phase offered a stronger boost and imparted significant protection [80]. The data also reinforces the fact that in most published vaccine studies, mice are challenged far too quickly [9] and the longer vaccination-to-challenge intervals, such as 6–8 months after BCG vaccination, will provide better information about the protective efficacy of preclinical vaccines against Mtb infection in the mouse model.…”

Mycobacterium tuberculosis adhesins: potential biomarkers as anti-tuberculosis therapeutic and diagnostic targets

“…The secreted antigen is not present in other mycobacterial species, including M. avium, M. marinum or M. smegmatis (Ragas et al, 2007;Nandakumar et al, 2013). Apa is targeted by, and binds directly to, the human PSP-A, an innate immune system C-type lectin responsible for early recognition of invading pathogens (Ragas et al, 2007).…”

“…Apa has been proposed as a possible vaccine candidate or component for future vaccines against TB. Nandakumar et al (2013) showed that Apa offered significant protection against virulent M. tuberculosis in mice when used as a BCG-booster vaccine.…”

Mycobacterial glycoproteins: a novel subset of vaccine candidates

“…Interestingly, the MS analyses identified 13 glycoproteins in Mtb CF in contrast to the 41 captured by affinity chromatography (González-Zamorano et al, 2009; Smith et al, 2014). Liu et al (2013) first linked a functional and virulent role to the Mtb mannosyl transferase membrane protein (Rv1002c) by establishing a Δ Rv1002c mutant.…”