Immune responses to Mycobacterium tuberculosis membrane-associated antigens including alpha crystallin can potentially discriminate between latent infection and active tuberculosis disease

Abstract

Changes in expression of membrane antigens may accompany the transition of Mycobacterium tuberculosis (Mtb) from 'dormant' to 'active' states. We have determined whether antibody and T cell responses to Mtb membrane (MtM)-associated antigens, especially the latency-induced protein alpha crystallin (Acr), can discriminate between latent tuberculosis infection (LTBI) and active TB (ATB) disease. Study subjects comprised a previously described cohort of healthcare workers (HCWs, n = 43) and smear-positive ATB patients (n = 10). HCWs were further categorized as occupational contacts (OC, n = 30), household contacts of TB (HC, n = 8) and cured TB (CTB, n = 5). Levels (ΔOD) of serum antibody isotypes (IgG, IgA and IgM) were determined by ELISA and blood T cell proliferative responses were determined by flow cytometry using Ki67 protein as marker for DNA synthesis. Antibodies to MtM and Acr were predominantly IgG and their levels in HCWs and ATB did not differ significantly. However, HCWs showed a significantly higher level of anti-MtM IgM and a significantly lower level of anti-Acr IgA antibodies than the ATB patients. Also, a larger proportion of HCWs showed a high (>1) ΔOD Acr /ΔOD MtM ratio for IgG. HCWs also showed a higher, though not significantly different from ATB, avidity of anti-MtM (IgG) antibodies. A higher proportion of HCWs (35% of OC, 62.5% of HC and 20% of CTB), compared with ATB (10%) showed a positive T cell response to Acr along with significant difference (P <0.05) between HC and ATB. A significant correlation (r = 0.60, P <0.0001) was noted between T cell responses of HCWs towards Acr and MtM (reported earlier by us) and both responses tended to decline with rising exposure to the infection. Even so, positive responses to Acr (38.5%) were significantly lower than to MtM (92%). Neither antibody nor T cell responses to either antigen appeared affected by BCG vaccination or reactivity to tuberculin. Results of the study suggest that the levels of IgM antibodies to MtM, IgA antibodies to Acr and

Patterns of T and B cell responses to Mycobacterium tuberculosis membrane-associated antigens and their relationship with disease activity in rheumatoid arthritis patients with latent tuberculosis infection

“…Mtb cell-membrane (MtM) was isolated by using a previously described protocol [ 17 ]. Briefly, 3–4 week old culture of Mtb (strain H37Ra, ATCC25177) was harvested and sonicated.…”

“…Cell lysate was differentially centrifuged to obtain membrane as sediment and cytosol as supernatant. Protein was estimated by the modified Lowry’s method [ 17 ] and aliquots were stored at -80°C. Identity of Mtb was ascertained by immune-chromatographic detection of MPT64 [ 17 ] using a kit (‘SD Bioline TB Ag MPT64 Rapid’, Abbott, USA).…”

“…Protein was estimated by the modified Lowry’s method [ 17 ] and aliquots were stored at -80°C. Identity of Mtb was ascertained by immune-chromatographic detection of MPT64 [ 17 ] using a kit (‘SD Bioline TB Ag MPT64 Rapid’, Abbott, USA). Recombinant Acr protein (LRP-0019C) was purchased from Lionex GmbH, Germany.…”

Diagnosis for Latent Tuberculosis Infection: New Alternatives

“…Individuals with established LTBI have higher plasma levels of anti-Rv2626c IgG than in recently infected individuals and patients with active TB (80). Levels of IgM antibodies against M. tuberculosis membraneassociated antigens (MtM), IgA antibodies against alpha crystallin (Acr), and a proliferative T-cell response to both antigens can potentially discriminate between LTBI and active TB disease (81).…”

“…▪ Levels of IgM antibodies against M. tuberculosis membrane-associated antigens (MtM), IgA antibodies against alpha crystallin (Acr), and a proliferative T-cell response to both antigens can potentially discriminate between LTBI and active TB disease ( 81 ).…”