Subepithelial B cells in the human palatine tonsil. II. Functional characterization.
This study investigates the main functional features of subepithelial (SE) B cells and compares them with those of purified germinal center (GC) and follicular mantle (FM) B cells isolated from the same tonsils. Unlike FM B cells, SE B cells failed to produce polyspecific antibodies in vitro; unlike GC B cells, SE B cells expressed high levels of Bcl-2 and failed to undergo spontaneous apoptosis in vitro. The most striking function of SE B cells was their ability to produce IgM antibodies to T cell-independent type-2 (TI-2) (but not to TI-1) antigens (Ag). These antibodies could not be detected when both FM and GC B cells were stimulated with TI-2 Ag in vitro. Moreover, B cells isolated from peripheral blood were unable to mount a response to TI-2 Ag. The latter finding is consistent with the observation that B cells with the phenotypic features of SE B cells were virtually absent in the peripheral blood and emphasizes the notion that SE B cells belong to a subset of non-recirculating B cells. SE B cells were by far superior to FM B cells in mixed lymphocyte reaction (MLR) stimulation of allogeneic T cells in vitro, although they were not as efficient as dendritic cells (DC). In order to stimulate T cells efficiently, SE B cells had to be exposed to anti-mu antibody, a treatment which induced expression of activation markers such as CD80, CD86, CD69 and CD39, usually absent in resting SE B cells. CD80 and CD86 molecules expressed by SE B cells participated in the chain of events required to promote the proliferation of allogeneic T cells as demonstrated by inhibition tests with the appropriate mAb. The expression of CD80 and CD86 by anti-mu-treated SE B cells was not, however, the sole explanation for their good antigen presenting capacities since the exposure of FM B cells to anti-mu antibody also induced expression of these surface structures. Nevertheless, these cells failed to become good MLR stimulators. Collectively, the above data contribute further to the characterization of a distinct subset of tonsillar B cells which resemble, both phenotypically and functionally, the B cells of the splenic marginal zone.
Dono
M
M
Servizio di Immunologia Clinica, Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy. manlio@igecuniv.cisi.unige.it
Zupo
S
S
Augliera
A
A
Burgio
V L
VL
Massara
R
R
Melagrana
A
A
Costa
M
M
Grossi
C E
CE
Chiorazzi
N
N
Ferrarini
M
M
D000818:Animals; D000917:Antibody Formation; D015703:Antigens, CD / Q000032:analysis; D017209:Apoptosis; D001402:B-Lymphocytes / Q000276:immunology / Q000502:physiology*; D006801:Humans; D008213:Lymphocyte Activation; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D010159:Palate / Q000276:immunology; D014066:Palatine Tonsil / Q000276:immunology*; D011518:Proto-Oncogene Proteins / Q000032:analysis; D019253:Proto-Oncogene Proteins c-bcl-2; D014301:Trinitrobenzenes / Q000276:immunology
D015703:Antigens, CD; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014301:Trinitrobenzenes