Human Germinal Center CD4
Human Germinal Center CD4 / CD57 / T Cells Act Differently On B Cells Than Do Classical T-Helper Cells
FARIDA BOUZAHZAH
ALAIN BOSSELOIR
ERNST HEINEN
LtON J. SIMAR
We have isolated two subtypes of helper T cells from human tonsils: CD4 CD57 cells, mostly located in the germinal center (GC), and CD4 CD57- cells, distributed through the interfollicular areas but also present in the GC. In a functional study, we have compared the capacities of these T-cell subtypes to stimulate B cells in cocultures. In order to block T-cell proliferation while maintaining their activation level, we pretreated isolated T cells with mitomycin C prior to culture in the presence of B cells and added polyclonal activators such as PHA and Con A, combined or not with IL-2. Contrary to CD4/CD57- cells, CD4 CD57 cells did not markedly enhance B-cell proliferation. Even when sIgD-B cells typical of germinal center cells were tested, the CD4 CD57 cells had no significant effect. This is in accordance with the location of these cells: They mainly occupy the light zones of the GC where few B cells divide. Even when added to preactivated, actively proliferating cells, CD4 CD57 cells failed to modulate B-cell multiplication. On the supernatants of B-cell-T-cell cocultures, we examined by the ELISA technique the effect of T cells on Ig synthesis. Contrary to CD57- T cells, whose effect was strong, CD57 T cells weakly stimulated Ig synthesis. More IgM than IgG was generally found. Because CD57 antigen is a typical marker of natural killer cells, we tested the cytolytic activity of tonsillar CD4/CD57 cells on K562 target cells. Unlike NK cells, neither CD4+CD57 nor CD4 CD57- cells exhibit any cytotoxicity. Thus, germinal center CD4 CD57 cells are not cytolytic and do not strongly stimulate either B-cell proliferation or Ig secretion. CD4 CD57- cells, however, enhance B-cell proliferation and differentiation, thus acting like the classical helper cells of the T-dependent areas.
Germinal center; T-helper cells; CD57 T cells; cell proliferation
INTRODUCTION
T lymphocytes purified from human tonsils are
mainly CD4 cells
(Sugiyama et al., 1976, 1984,
1987; Plum et al., 1987)
, CD8 T cells being
proportionally less numerous in tonsils than in the
peripheral blood (Sugiyama et al., 1987). The
prevalence of CD4 cells in tonsils suggests that tonsillar
T lymphocytes are functionally oriented to helper
activity
(Sugiyama et al., 1987)
. Several
immunohistochemical studies have revealed the existence of
tonsillar T cells expressing the CD57 antigen
characteristic of cells with NK activity
(Okada et al.,
1988)
. These cells are essentially located in the GC
light zone; a few are also found in the interfollicular
T-dependent areas and the mantle zones
(Bouzahzah et al., 1993)
. In a previous ultrastrutural
morphological study, we have shown that these
cells are medium-sized and do not contain the large
granules typical of blood NK cells
(Bouzahzah et al.,
1993)
. Phenotypically, these cells do not express Leu
8, CD16, or CD11b, so they clearly differ from
classical NK cells
(Si and Whiteside, 1983; Verlardi
et al., 1985, 1986a)
. These CD4
CD57
cells do not
express CD25 (IL-2 receptor), CD71 (transferrin
receptor), or HLA-DR, but do express CD69 (Bowen
et al., 1991). Thus, they should be viewed as
preactivated rather than fully activated cells. Their
to much debated
ability produce cytokines is
(Velardi et al., 1986b;
Bosseloir et al., 1989
, 1991;
There is no available data as to the function of
CD4 /CD57 /cells. In this report, we compare the
effects of CD4 CD57 and CD4 CD57- cells on
B-cell proliferation and differentiation in
Igsecreting cells. Using several procedures (nylon
wool columns, and selections by dynabeads and
MACS), we have purified both populations of
Thelper cells and cocultured them with B cells
isolated from tonsils. We have compared the capacity
of B cells to incorporate tritiated thymidine or to
produce IgM or IgG in these two types of coculture.
We pretreated the T-cell populations with
mitomycin C to prevent their multiplication but added
various activators to the cultures. In another series
of experiments, we tested the cytotoxicity of
CD4 CD57- and CD4 CD57 in the presence of
K562 target cells.
11000.
8800
000
4400
2200
o/
RESULTS
Effects of CD57
Proliferation
and CD57- T Cells on B-cell
To test the effects of CD57 and CD57- cells on
B-cell proliferation, cell populations enriched in
these cells were added to highly purified B cells. The
purity of the T-cell populations used, as estimated
by flow cytometry, exceeded 94% (CD57 cells) or
96% (CD57- cells). Before being cocultured, the
T-cell populations were treated with mitomycin C to
minimize their capacity to incorporate
[3H]thymidine. The cells were stimulated, however,
with PHA (2 tg/ml) to keep them activated. As a
control, B cells were cultured alone. Little or no
proliferative activity was observed in B-cell
populations cultured alone or in mitomycin (...truncated)