IFN-g and IL-5 whole blood response directed against mycolactone polyketide synthase domains in patients with Mycobacterium ulcerans infection
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Date
2018-07-31
Journal Title
Journal ISSN
Volume Title
Publisher
PeerJ
Abstract
Background: Buruli ulcer is a disease of the skin and soft tissues caused by infection
with a slow growing pathogen, Mycobacterium ulcerans. A vaccine for this disease is
not available but M. ulcerans possesses a giant plasmid pMUM001 that harbours
the polyketide synthase (PKS) genes encoding a multi-enzyme complex needed for
the production of its unique lipid toxin called mycolactone, which is central to the
pathogenesis of Buruli ulcer. We have studied the immunogenicity of enzymatic
domains in humans with M. ulcerans disease, their contacts, as well as non-endemic
areas controls.
Methods: Between March 2013 and August 2015, heparinized whole blood was
obtained from patients confirmed with Buruli ulcer. The blood samples were diluted
1 in 10 in Roswell Park Memorial Institute (RPMI) medium and incubated for 5 days
with recombinant mycolactone PKS domains and mycolyltransferase antigen 85A
(Ag85A). Blood samples were obtained before and at completion of antibiotic
treatment for 8 weeks and again 8 weeks after completion of treatment. Supernatants
were assayed for interferon-g (IFN-g) and interleukin-5 (IL-5) by enzyme-linked
immunosorbent assay. Responses were compared with those of contacts and
non-endemic controls.
Results: More than 80% of patients and contacts from endemic areas produced
IFN-g in response to all the antigens except acyl carrier protein type 3 (ACP3) to
which only 47% of active Buruli ulcer cases and 71% of contacts responded. The
highest proportion of responders in cases and contacts was to load module ketosynthase domain (Ksalt) (100%) and enoylreductase (100%). Lower IL-5
responses were induced in a smaller proportion of patients ranging from 54% after
ketoreductase type B stimulation to only 21% with ketosynthase type C (KS C).
Among endemic area contacts, the, highest proportion was 73% responding to KS C
and the lowest was 40% responding to acyltransferase with acetate specificity type 2.
Contacts of Buruli ulcer patients produced significantly higher IFN-g and IL-5
responses compared with those of patients to PKS domain antigens and to
mycolyltransferase Ag85A of M. ulcerans. There was low or no response to all the
antigens in non-endemic areas controls. IFN-g and IL-5 responses of patients
improved after treatment when compared to baseline results.
Discussion: The major response to PKS antigen stimulation was IFN-g and the
strongest responses were observed in healthy contacts of patients living in areas
endemic for Buruli ulcer. Patients elicited lower responses than healthy contacts,
possibly due to the immunosuppressive effect of mycolactone, but the responses were
enhanced after antibiotic treatment. A vaccine made up of the most immunogenic
PKS domains combined with the mycolyltransferase Ag85A warrants further
investigation.
Description
An article published by PeerJ and available at DOI 10.7717/peerj.5294
Keywords
Microbiology, Immunology, Infectious Diseases
Citation
PeerJ, DOI 10.7717/peerj.5294