The mechanisms of host immune responses
in melioidosis are poorly understood. The present
study demonstrated that in vitro exposure of PBMC
to virulent B. pseudomallei as well as avirulent B.
thailandensis stimulated IL-17 mRNA and protein
expression by PBMC. As IL-17 has been shown to
be essential in antigen-specific T cell responses2, this
cytokine should play a significant role in the response
to infection with these bacteria. Moreover, in
the diabetic patients, of which 8/10 had elevated
HbA1c suggesting a poorly controlled disease, levels
of both mRNA and protein of IL-17 were lower. In
addition, the present study showed that both B. pseudomallei
and B. thailandensis caused reduced IL-23
mRNA expression in the PBMC. Although IL-23
has been thought to promote IL-17 synthesis11, recent
works have shown that in the presence of other
cytokines, namely IFN-γ and IL-4, the expression of
IL-17 can not be enhanced by IL-2312,13. Thus, it appears
that the IL-17 expression of PBMC stimulated
by Burkholderia spp. in the present study was not directly
associated with IL-23. IL-6 has also been
shown to be increased in mice and humans infected
with B. pseudomallei 14,15 and this cytokine may be
involved in the induction of IL-17 expression16.
However, several other yet unidentified factors could
also be involved in the control of IL-17 expression in
melioidosis.
It is possible