Lamina propria T cells have a low expression of the CD45RA antigen and a high expression of the CD45RO antigen. This phenotype
is characteristic for memory T cells (table 2). In addition, T cells in the effector compartment of the mucosa bear surface
antigens which are very rarely found in other sites of the immune system. Intestinal T cells also express functional IL-2
receptors and IL-2 receptor α chain mRNA, and are able to synthesize high amounts of IL-2. However, another marker of memory
T cells, CD29, is not expressed in high density in the lamina propria indicating that lamina propria T cells differ from ‘classical’
memory T cells. This is supported by functional studies in nonhuman primates infected rectally with
C. trachomatis which show that lamina propria T cells do not proliferate after stimulation with antigen but rather provide helper function
for immunoglobulin synthesis (table 2).
The intestinal lamina propria therefore contains highly specialized T cells which have a distinctive phenotype and are activated.
Functionally these T cells can be characterized as differentiated effector lymphocytes which respond to triggering the antigen-specific
T cell receptor by secreting helper factors for B cells. This concept is supported by recent studies showing that the pattern
of lymphokines produced by lamina propria T cells and the responsiveness to certain lymphokines differ from those of other
lymphocyte populations [25]. Lamina propria T cells thus represent a subset of memory T cells with a unique maturational state.
Dedicated to professor Dr. Wolfgang Gerok, Freiburg, FRG, on the occasion of his 65th birthday.
Supported by a grant from the ‘Deutsche Forschungsgemeinschaft’ (Ze 188/4-2).