Serological Evaluation of Mycobacterium ulcerans Antigens Identified by Comparative Genomics

Abstract

A specific and sensitive serodiagnostic test for Mycobacterium ulcerans infection would greatly assist the diagnosis of Buruli ulcer and would also facilitate seroepidemiological surveys. By comparative genomics, we identified 45 potential M. ulcerans specific proteins, of which we were able to express and purify 33 in E. coli. Sera from 30 confirmed Buruli ulcer patients, 24 healthy controls from the same endemic region and 30 healthy controls from a non-endemic region in Benin were screened for antibody responses to these specific proteins by ELISA. Serum IgG responses of Buruli ulcer patients were highly variable, however, seven proteins (MUP045, MUP057, MUL_0513, Hsp65, and the polyketide synthase domains ER, AT propionate, and KR A) showed a significant difference between patient and non-endemic control antibody responses. However, when sera from the healthy control subjects living in the same Buruli ulcer endemic area as the patients were examined, none of the proteins were able to discriminate between these two groups. Nevertheless, six of the seven proteins showed an ability to distinguish people living in an endemic area from those in a non-endemic area with an average sensitivity of 69% and specificity of 88%, suggesting exposure to M. ulcerans. Further validation of these six proteins is now underway to assess their suitability for use in Buruli ulcer seroepidemiological studies. Such studies are urgently needed to assist efforts to uncover environmental reservoirs and understand transmission pathways of the M. ulcerans.

Buruli ulcer

“…1,8,24,30,60 This has led to improved therapy, 61,62 as well as identification of possible candidates for vaccination and diagnosis. 26,28,51 However, many questions remain to be answered, such as the relative importance of humoral and cellular immune responses in controlling the infection. Both responses most likely contribute to control of infection, although their relative role may depend on the stage of infection.…”

“…With this information, many M. ulceransspecific proteins have recently been identified and shown to be immunogenic. 28 In addition, there are many proteins with strong homology to other mycobacterial proteins, such as antigen 85A (Ag85A) that shows an 84% amino acid sequence identity to Ag85A from M. tuberculosis. 26 Indeed, Tanghe et al showed that a DNA vaccine coding for Ag85A from either M. tuberculosis or M. ulcerans was able to delay BU progression in mice, with DNA encoding Ag85A from M. ulcerans giving significantly more protection than DNA encoding Ag85A from M. tuberculosis.…”

“…30 Random transposon mutagenesis has also revealed other genes necessary for toxin production. 30,31 Pidot et al 28 have shown that BU patients and persons that have been exposed to M. ulcerans, but who remain disease free, can make antibodies against several of the PKS enzymatic domains. On the other hand, it remains to be demonstrated if antibodies can access the synthases in bacteria to prevent toxin production and if this can prevent BU.…”

“…Some of these are unique to M. ulcerans while others share homology with other mycobacteria. [26][27][28] A range of potential targets, coupled with recent improvements in the field of vaccine development, offers a wide variety of vaccine candidates and delivery techniques against M. ulcerans. Some of these are discussed below and summarized in Table 1. ©2 0 1 1 L a n d e s B i o s c i e n c e .…”

“…Recent work has shown that people can be exposed to and develop immune responses against M. ulcerans without developing disease symptoms. 28 Furthermore, people can spontaneously heal lesions without treatment, although a deforming scar can remain. 63 This indicates that an adaptive immune response, whether it is humoral, cellular or both, is able to control and clear the infection.…”