External Capsule Protects Gum Disease-Causing Bacteria From Immune Response
The capsule of Porphyromonas
gingivalis, the bacterium that causes gum disease, provides stealth,
boosting the bacterium’s virulence, according to a paper published in the
November Infection and Immunity. Call
it a sugar coating, if you will, for in fact, the capsule is made from sugar
molecules, which do not ordinarily elicit immunity. Thus it hides the
bacterium’s proteins within, preventing immune response.
In the study, the researchers, led by Janina P. Lewis of
Virginia Commonwealth University, Richmond, compared the ability of normal, and
mutant bacteria that were missing the capsule, to activate the immune system,
to enter eukaryotic cells (the kind that are present in multicellular
organisms), to cause disease, and to survive in mice. “The mutant bacteria
activated the host to a greater extent, and thus, were more easily killed by
eukaryotic cells,” says Lewis. “Thus, the capsule protects the bacteria and
allows them to survive unnoticed in our bodies.”
Capsules also protect both bacteria and fungi, including P. gingivalis, as per this report, from
being engulfed by the immune system’s phagocytes (phago=eat; cyto=cell) and
from being identified by dendritic cells as dangerous, thus marking them for
destruction by antibodies. Conversely, in the study, mutant, non-encapsulated P. gingivalis were rapidly engorged by
immune cells, and killed.
“Thus, anything that would interfere with generation of
capsule, such as drugs interfering with the action of enzymes involved in
synthesis of the sugar coat, could be used in treatment of periodontal disease,
and importantly, could have broader implications for prevention of more serious
diseases,” by other encapsulated bacteria, such as pneumonia, anthrax,
meningitis, endocarditis, and gastroenteritis, says Lewis.
(A. Singh, T. Wyant, C. Anaya-Bergman, J. Aduse-Opoku, J.
Brunner, M.L. Laine, M.A. Curtis, and J.P. Lewis, 2011. The capsule of Porphyromonas gingivalis leads to a
reduction in the host inflammatory response, evasion of phagocytosis, and
increase in virulence. Infect. Immun. 79:4533-4542.)
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