Antigen-specific secretion of IFNγ and CXCL10 in whole blood assay detects Mycobacterium leprae infection but does not discriminate asymptomatic infection from symptomatic leprosy.

To advance toward a whole blood assay (WBA)-based test capable of facilitating the diagnosis of paucibacillary (PB) leprosy, we evaluated a prototype in-tube WBA using combinations of Mycobacterium leprae antigens. Blood was collected from newly diagnosed untreated PB (n=38), multibacillary (MB) (n=30), healthy household contacts (HHC) of MB (n=27), and endemic controls (n=61) residing in Goiânia and Fortaleza, Brazil. Blood was incubated with M. leprae cell sonicate, recombinant proteins (46f+LID-1; ML0276+LID-1), or controls (phosphate-buffered saline, phytohemagglutinin, M. tuberculosis purified protein derivative). Antigen-specific IFNγ production was observed in 71-84% and 55% of PB and HHC, respectively. Antigen-specific CXCL10 levels were similarly assessed to determine if, unlike IFNγ, CXCL10 could differentiate PB from HHC with repeated exposure/asymptomatic M. leprae infection. The CXCL10 levels induced in response to M. leprae antigens could not, however, differentiate PB from HHC. Despite these limitations, the WBAs reported here still represent important tools for assessing M. leprae infection rates and evaluating the impact of control measures.

Application of Mycobacterium Leprae-specific cellular and serological tests for the differential diagnosis of leprosy from confounding dermatoses.

Mycobacterium leprae-specific serological and cell-mediated-immunity/CMI test were evaluated for the differential diagnosis of multibacillary/MB, and paucibacillary/PB leprosy from other dermatoses. Whole-blood assay/WBA/IFNγ stimulated with LID-1 antigen and ELISA tests for IgG to LID-1 and IgM to PGL-I were performed. WBA/LID-1/IFNγ production was observed in 72% PB, 11% MB leprosy, 38% dermatoses, 40% healthy endemic controls/EC. The receiver operating curve/ROC for WBA/LID-1 in PB versus other dermatoses showed 72.5% sensitivity, 61.5% specificity and an area-under-the-curve/AUC=0.75; 74% positive predictive value/PPV, 59% negative predictive value/NPV. Anti PGL-I serology was positive in 67% MB, 8% PB leprosy, 6% of other dermatoses; its sensitivity for MB=66%, specificity=93%, AUC=0.89; PPV=91%, NPV=72%. Anti-LID-1 serology was positive in 87% MB, 7% PB leprosy, all other participants were seronegative; 87.5% sensitivity for MB, 100% specificity, AUC=0.97; PPV=100%, NPV=88%. In highly endemic areas anti-LID-1/PGL-I serology and WBA/LID-1-represent useful tools for the differential diagnosis of leprosy from other confounding dermatoses.