MICROENVIRONMENT INFLUENCE GALT LOCATION AND ONTOGENY

Macroscopic nodules of gut associated lymphoid tissue (GALT) are
distributed over the length of the gastrointestinal tract.
However, their frequency at some sites is greater than can be
accounted for by random distribution. Similarly, anodular areas
also occur at specific sites. Such a non-random distribution of
GALT suggests the presence of a microenvironmental/stromal element
in both the small and large intestine, which may play a role in the
formation and localization of GALT. In addition, grafts of fetal
intestine from areas of high GALT frequency develop normal
lymphoid architecture with associated stroma when transplanted
ectopically, even in the absence of luminal antigen. Although
their role is not yet clear, stromal cells associated with GALT may
play an important role in the formation, localization and function
of this component of the immune system. It is the objective of
this proposal to better characterize this stromal population. To
do this, we will use light and electron microscopy along with
immunohistochemical techniques, while taking advantage of the
steroid sensitivity of the lymphocytes with proximal colonic
lymphoid tissue to enrich for stromal elements. We will examine
the ontogeny of these stromal elements, to determine whether they
are intrinsic to sites of high GALT frequency or whether they are
an immigrant population. We propose that location, development and
cellular composition of these nodules are microenvironmentally
determined. To test this, we will transplant small pieces of fetal
gut from sites which we predict will develop lymphoid nodules,
versus adjacent anodular regions, under the kidney capsule of
syngeneic recipients and evaluate the yield of nodules from the
former vs the latter. We will attempt to purify GALT stromal
elements utilizing techniques of low temperature organ culture and
deoxyguanosine treatment to deplete lymphocytes. We have had
considerable success with these techniques in the purification of
thymic epithelium, and predict similar results with GALT stroma.
Finally, we will examine the origin of the lymphoid component of
GALT using grafts of fetal gut or purified GALT stroma. Grafts
will be placed into chimeric mice which have distinguishable
allelic isotypic markers and evaluated using flow cytometry and
immunohistochemistry. These studies will provide a more complete
understanding of GALT microenvironments and their role in the
ontogeny and localization of GALT. Clearly, these studies may be
important in the understanding of a variety of clinical situations
including digestive and autoimmune disorders, intestinal
transplantation, as well as tumors arising in GALT.