Transfer of the LKV39 4.5 cell line produced less intraocular
inflammation with a later peak than did LKOV39 1.8 and resulted in the
recruitment of CD8
+ T cells into the choroid,
iris, and limbus. The CD8
+ T-cell recruitment
appeared to be dependent on specific features of the LKOV39 4.5 T-cell
line, because CD8
+ T cells constituted only an
insignificant part of the infiltrate caused by LKOV39 1.8 T-cell
transfer. The T-cell lines, although cross-reactive with hr44, may
differ in the affinity of their T-cell receptor (TCR) for the rat 44
epitope, whereby the LKOV39 4.5 T-cell line may have the
appropriate affinity that leads to recruitment of
CD8
+ T cells to assert regulatory functions.
Suppressor CD8
+ T cells are known to play a role
in the regulation of autoreactive T cells in the experimental allergic
encephalomyelitis (EAE) mouse model
39 and have been shown
to be more frequent in Fisher rats resistant to EAE induction than in
the susceptible Lewis rat.
40 Specific surface structures
expressed by activated T cells appear to be involved in the induction
of CD8
+ T cell differentiation into effectors to
delete or inactivate self-reactive T cells.
41 42 It is
suggested that CD8
+ T cells recognize activated
alloreactive or self-reactive CD4
+ T cells in a
Qa-1–restricted manner, implicating the recognition of TCR peptides by
CD8
+ T cells in the context of MHC class 1b
molecules expressed on activated CD4
+ T
cells.
43 44 The functions of CD4
+ T
cells recognized in such a way are thought to be moderated by the
suppresser cell, either by direct cytotoxicity or by release of
cytokines. MHC class 1b molecules in the rat have been
identified,
45 including RT1-U2, which, similar to the
mouse Qa-1, can be recognized as a target by cytotoxic T
cells.
46 Specific surface molecules expressed on the
LKOV39 1.8 and -4.5 T-cell lines and their respective affinities for
rat 44 remain to be identified. The maintenance of tolerance by
regulatory CD8
+ cells is aided by the expression
of FasL on ocular tissue, which can induce apoptosis of infiltrating
Fas
+ leukocytes.
47 It is of interest
that elevated numbers of possibly regulatory CD8
+ T cells have been reported in conjunctival biopsy tissue of patients
with onchocerciasis.
48 Numbers of
CD4
+ T cells detected in ocular tissues of rats
that received the LKOV39 T-cell lines reached statistical significance
only when compared with those in normal subjects in the limbus.