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Study of mucosal immune responses |
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Principal Investigator : Anna George Project Associate Ph D Students Collaborators The aim of the research projects of this laboratory is
to analyze events in B and T cell activation and differentiation, with some
emphasis on the interface between mucosal and systemic immunity. A number of
related experimental approaches are being used to address the main aim. One
approach, that directly addresses interactions between mucosal and systemic
immunity, involves dissecting the consequences and mechanism of oral tolerance
to soluble antigens of microbial and non-microbial origin. Other approaches
address the role of specific ligand-receptor interactions in B cell activation
and differentiation, designing ways of enhancing the immunogenecity of orally
administered antigens, and analyzing signals that may contribute to the
selective differentiation of B and T cells to immediate effectors versus
memory cells. Oral tolerance In our
analysis of the systemic consequences of orally encountered soluble bacterial
antigens in BALB/c mice, we have reported that oral tolerance, read out as T
cell hyporesponsiveness to recall antigen in vitro, could be induced with
S.aureus and L.major sonicates, but not with S.typhimurium sonicate. We have
now looked at the consequences of feeding-associated T cell hyporesponsiveness
on antibacterial immunity and we report that in vitro T cell
hyporesponsiveness does not correlate strictly with the ability of fed mice to
clear a challenge infection with virulent organisms. Thus, while T cells from
BALB/c mice fed with S.typhimurium sonicate did not respond better in vitro
than unfed mice, they cleared a homologous challenge infection better than
unfed mice did. On the other hand, mice fed with S.aureus sonicate responded
far poorly than unfed mice in vitro but they were not severely compromised in
their ability to clear a homologous challenge infection. These data, together
with the results on cytokine KO mice reported last year, suggest that a
complex and subtle relationship exists between Th1/Th2 cytokine balances and
the induction and maintenance of systemic T cell hyporesponsiveness on the one
hand and induction of anti-bacterial immunity on the other. To dissect this out,
we have also compared clearance of the two bacterial pathogens in four
different KO mouse strains that include Th1/Th2 cytokine deficiency (IL-4,
IL-10 and IFNgKOs), and TCRgd
cell deficiency (TCRd KO). We find that oral administration
of the two sonicates has quite distinct effects on bacterial clearance. At
appropriate challenge doses, fed wild-type C57BL/6 mice do not clear S.aureus
challenge as well as unfed controls do and this pattern is seen in the all
four KO strains. On the other hand, fed wild-type C57BL/6 mice clear S.typhimurium
challenge better than unfed mice and this pattern is seen in IL-4, IL-10 and
TCRd-KO mice but not in IFNg
KO mice. S.aureu is an
extracellular, non-enteric pathogen that is effectively cleared by antibodies
generated with the help of Th2 cytokines and S.typhimurium is an
intracellular, enteric pathogen that is cleared by a combination of
antibodies, activated macrophages and cytotoxic T cells, with contributions
from Th1 and Th2 cytokines. We have now initiated experiments to look at the
clearance of L.major, an intracellular non-enteric pathogen that requires a
Th1-dominated response for parasite clearance in these KO mouse strains.
L.major sonicate behaves like S.aureus sonicate in inducing oral tolerance as
read out by T cell recall responses in vitro, and these experiments should be
useful in helping us dissect out the interplay between oral feeding and
cytokine balances in systemic anti-microbial immunity. B and T cell activation and differentiation Over the current
reporting year, we have analyzed the effect of CD27 ligation on B cell
responses in vivo. We report that primary antibody responses are poorer in
mice immunized with a T-dependent antigen in the presence of anti-CD27 than in
control mice. Thus, ligation of CD27 in vivo during B cell priming inhibits
plasma cell generation, as seen with in the in vitro B cell activation systems
reported last year. Since plasma cell generation and memory cell generation
are mutually exclusive consequences of B cell activation, these data raise the
possibility that the reduced terminal differentiation that occurs in the
presence of anti-CD27 may be accompanied by an enhanced memory cell pool. We
have initiated experiments to test this possibility. We have also been
analysing the effect of ICAM-1 deficiency on B and T cell maturation and
priming. We report that in ICAM-1 KO mice, B cell maturation is normal as
assessed by proportions of mature and immature B cells in the periphery.
However, they have relatively more B cells in the spleen than wild-type mice,
suggesting that export and/or survival of the cells may differ. Polyclonal
responses to LPS and immunoglobulin cross-linking are similar when normalized
for B cell numbers, but preliminary experiments indicate that they may respond
less well to surface IgM crosslinking. We have also found that while T cells
in the KO mice do get primed following immunization, recall responses decay
faster than in wild-type mice. The data suggest that persistence of primed
cells or generation of memory T cells may be compromised in these mice. Publications Original peer-reviewed articles 1.
Raman VS, Bal V, Rath S and George A (2000). Ligation of CD27
on murine B cells responding to T-dependent and T-independent stimuli inhibits
the generation of plasma cells. J Immunol 165:6809-6815. 2.
Pasare C, Mukherjee P, Verhoef A, Bansal P, Mendiratta SK,
George A, Lamb JR, Rath S and Bal V (2001) T cells in mice expressing a
transgenic human T cell receptor b chain get positively selected but cannot be
activated in the periphery by signaling through T cell receptor. Int Immunol
13:53-62. |