Apoptosis of ileal Peyer's patch B cells is increased by glucocorticoids or anti-immunoglobulin antibodies.
The ileal Peyer's patch (PP) in sheep plays a central role in the development and production of B cells. Associated with a tremendous amount of B cell proliferation in this site is the extensive diversification of the Ig repertoire by somatic hypermutation. Very few (< 5%) of the B cells produced in the ileal PP differentiate and emigrate; instead, the vast majority of these cells soon die, and we have previously shown that death is associated with apoptosis. When placed in culture, ileal PP B cells die rapidly by apoptosis, such that after 24 h, 60 +/- 1% of DNA is fragmented. Here, we show that the extent of this spontaneous B cell apoptosis in culture, as quantitated by DNA fragmentation, was significantly increased in a dose-dependent manner by the glucocorticoids hydrocortisone or dexamethasone. Furthermore, treatment of lambs with 2-2.5 mg/kg of dexamethasone resulted in a marked increase in the number of apoptotic cells in the ileal PP and an increase in ileal PP B cell DNA fragmentation to 20 +/- 6%, compared with 2.4 +/- 0.1% in untreated lambs. Anti-immunoglobulin (Ig) antibodies also increased the extent of DNA fragmentation in cultured ileal PP B cells. After 24 or 48 h of culture with anti-Ig (PIg47A), DNA fragmentation was 74 +/- 2% and 75 +/- 3%, respectively. Ileal PP B cells are rescued from apoptosis by agents that activate protein kinase C and increase cytosolic Ca2+, and here we show that this treatment also results in apoptotic rescue in the presence of dexamethasone or anti-Ig. We speculate that the apoptosis of ileal PP B cells in situ may be modulated by glucocorticoids and by the cross-linking of surface Ig. Apoptosis, induced by a signal through surface Ig, may be an important mechanism in the deletion of self-reactive B cells during the expansion of the Ig repertoire in the ileal PP.
Motyka
B
B
Department of Medical Physiology, University of Calgary, Canada.
Bhogal
H S
HS
Reynolds
J D
JD
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology*; D017209:Apoptosis; D001402:B-Lymphocytes / Q000166:cytology*; D002118:Calcium / Q000502:physiology; D004249:DNA Damage; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology*; D007082:Ileum / Q000166:cytology; D066298:In Vitro Techniques; D008297:Male; D010581:Peyer's Patches / Q000166:cytology*; D011493:Protein Kinase C / Q000502:physiology; D012756:Sheep
D000888:Antibodies, Anti-Idiotypic; D005938:Glucocorticoids; D011493:Protein Kinase C; D002118:Calcium