INVESTIGADORES
DE MORENO Maria Alejandra
artículos
Título:
Proposed model: mechanisms of immunomodulation induced by probiotic bacteria.
Autor/es:
C. MALDONADO GALDEANO; A. DE MORENO DE LEBLANC; C.G. VINDEROLA; M.E. BIBAS BONET; G. PERDIGON
Revista:
CLINICAL AND VACCINE IMMUNOLOGY
Editorial:
American Society for Microbiology
Referencias:
Lugar: Washington, USA; Año: 2007 vol. 14 p. 485 - 492
ISSN:
1556-6811
Resumen:
The mammalian microbiota comprises several hundred different
bacterial species, many of which have a beneficial effect
on the host. For example, they are involved in preventing
colonization of the gut by pathogens and maintaining the gut
mucosal immunity (85). The gut microbiota is more abundant
in the large intestine of mammals, with densities rising to over
1011 organisms/g intestinal content (84, 86). The number of
bacterial cells in the entire gut exceeds the number of eukaryotic
cells in the host, but under normal circumstance they
coexist without any adverse effect on the host. The influence of
the resident microflora on mucosal immune function and gut
health has become an area of scientific and clinical importance
(22, 26). There is an active dialogue between the commensal
microorganisms and the host mucosal immune system (21, 48).
This cross talk elicits different host responses to commensal
and pathogenic bacteria. Commensal bacteria may even share
molecular patterns recognized by toll-like receptors (TLRs),
which can recognize patterns associated mainly with pathogens.
However, the mucosal immune system of the healthy
intestine allows the persistence of this microbiota associated
with the intestine and avoids immunological tolerance, maintaining
the intestinal homeostasis. Now, there is acceptance of
the concept that oral tolerance is not generated by commensal
intestinal bacteria; the host would ignore or fail to recognize
the presence of indigenous microorganisms (49). The healthy
host is able to elicit a good mucosal immune response against
luminal antigens and to maintain a physiological state of in-
flammation in the gut, but it is also capable of responding to
invading commensal organisms or pathogens. In the healthy
host the penetration of the commensal bacteria is usually prevented
by the barrier afforded by the intestinal epithelium and
the immune cells associated with the mucosa, which are highly
adapted to the presence of the normal microbiota (71). The
signals sent by these microorganisms prevent their penetration
and keep them outside the intestinal tissue. If the commensal
microorganisms invade the host tissues, the innate immune
mechanisms contribute to their rapid clearance, but when
pathogens enter the intestine, innate and adaptive mechanisms
are coordinately stimulated to respond to the danger signals
(38, 60). Although mucosal epithelial tissues form an efficient
barrier that prevents the entrance of the environmental pathogens
and the external antigens into the host internal milieu,
mucosal tissues represent the main sites of infection by pathogens.
Many attempts have been made to understand the gut
immunomodulation by pathogenic bacteria but not the mechanisms
involved in the modulation of the gut immune system
by commensal bacteria and by nonpathogenic microorganisms
present in many foods included in the daily diet.