Role of stromal cells and their products in protecting young and aged B-lineage precursors from dexamethasone-induced apoptosis.

Bone marrow stromal cells are potent providers of stimuli that induce proliferation of B-cell precursors. We proposed that stromal cells play a role in protecting B-lineage cells from corticosteroid-induced apoptosis. We found that stromal cells protected B-cell precursors from dexamethasone-induced apoptosis, but this did not strictly correlate with interleukin-7 (IL-7) production. To determine if stromal-derived factors were involved in protection of B-cell precursors from apoptosis, we examined the activity of three lymphopoietic growth factors: IL-7, stem cell factor (SCF), and insulin-like growth factor-1 (IGF-1). Either IL-7 or IGF-1 alone protected B-cell precursors from dexamethasone-induced apoptosis. The combined activities of IGF-1 and IL-7 were additive rather than synergistic. SCF did not protect B-cell precursors from apoptosis. Aging altered the ability of B-cell precursors to respond to protective stimuli induced by IL-7 and IGF-1. Precursors from aged animals were deficient in ability to modulate expression of apoptosis regulatory genes Bax, Bcl-2, and Bcl-x in comparison to B-cell precursors from young animals. Taken together, these results suggest that stromal cells can protect B-lineage precursors from a corticosteroid-induced apoptotic signal, protection is mediated by stromal-derived cytokines, and aging decreases the ability of B-cell precursors to respond efficiently to protective stimuli.

The avian chB6 alloantigen induces apoptosis in DT40 B cells.

In avian species, B-lymphocytes develop in the bursa of Fabricius. Cells developing in the bursa are subject to signals regulating their survival, with the majority of cells dying by apoptosis within the bursa. However, the molecules delivering the signals influencing this life and death decision remain enigmatic. We have previously shown that antibodies against the chB6 alloantigen present on avian B-lymphocytes can induce a rapid form of cell death. Here we extend this finding by showing that anti-chB6 antibodies induce true apoptosis in DT40 cells without visible membrane damage. This apoptosis results in DNA degradation and morphologic changes characteristic of apoptosis. Furthermore, this apoptosis is coincident with a loss of mitochondrial membrane potential and is inhibited by either overexpression of bcl-x(L) or the presence of inhibitors of caspase 8, 9, or 3 activity. Collectively these data argue that chB6 may function as a novel death receptor on avian B-lymphocytes and support the use of DT40 as an amenable model to study the signaling involved in chB6-induced apoptosis.

Age-related differences in the immune response to immunization with human Abeta42 peptide.

Several studies show that plaque burden is resolved in young to middle-aged amyloid precursor protein transgenic mice after rigorous immunization with Abeta42 peptide. We determined if wild-type 20-month-old and 3-month-old animals could produce high-titer antibody against Abeta42 with a less strenuous immunization protocol. All treated young animals mounted a high-titer (20,000-50,000) response after two immunizations and sustained a strong response for 6 months following the initial treatment with Abeta42. However, 6 of 8 immunized aged animals did not respond after three immunizations. The 2 responding aged mice produced low-titer antibody (5,000-10,000), which rapidly declined to control levels within 5 weeks after the third immunization. Aged animals may require alternate strategies for successful vaccination, such as inclusion of stimulatory cytokines or better adjuvants. If tolerance to Abeta42 underlies the poor response observed in aged animals, then a mechanism to overcome this response will have to be investigated.

The avian ChB6 alloantigen triggers apoptosis in a mammalian cell line.

Many developing B lymphocytes are deleted by apoptosis. However, the mechanism signaling their demise remains poorly understood. Like mammals, chicken B cells are selected during their development; >95% of the cells in the bursa of Fabricius die without entering the secondary immune system. The molecule chB6 (Bu-1) has been used as a marker to identify B cells in the chicken. ChB6 is a type I transmembrane glycoprotein whose function is enigmatic. We have provided evidence that chB6 can induce a rapid form of cell death exhibiting characteristics of apoptosis. Here we further examine cell death induced by chB6 in a transfected mouse cell line. ChB6 is shown to cause apoptosis in this cell line as detected by a TUNEL assay for DNA fragmentation. This apoptosis is subject to regulation by signals from growth factor or by Bcl-x(L). Furthermore, we show that Ab binding to chB6 leads to cleavage of caspase 8, caspase 3, and poly(ADP ribose) polymerase. Overall, these data support the hypothesis that chB6 is a novel death receptor on avian B cells.