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Decline in cellular immunity in aging compromises protection against infectious diseases and leads to the increased susceptibility of the elderly to infection. In particular, Ag-specific cytotoxic T lymphocyte (CTL) response against virus is markedly reduced in an aged immune system. It is of great importance to explore novel strategy in eliciting effective antiviral CTL activity in the elderly. In this study, the efficacy and mechanisms of immunization with immune complexes in overcoming age-associated deficiency in cellular immunity were investigated. In this study, we show that the severely depressed CTL response to influenza A in aged mice can be significantly restored by immunization with immune complexes consisting of influenza A virus and mAb to influenza A nucleoprotein. The main mechanisms underlying this recovery of CTL response induced by immune complex immunization in aged mice are enhanced dendritic cell function and elevated production of IFN-γ in both CD4+ Th1 and CD8+ CTLs. Thus, these results demonstrate that immune complex immunization may represent a novel strategy to elicit effective virus-specific cytotoxic response in an aged immune system, and possibly, to overcome age-related immune deficiency in general.

In aging, both primary and secondary antibody responses are impaired. One of the most notable changes in age-associated immune deficiency is the diminished germinal center (GC) reaction. This impaired GC response reduces antibody affinity maturation, decreases memory B cell development, and prevents the establishment of long-term antibody-forming cells in the bone marrow. It is of great importance to explore novel strategy in improving GC response in the elderly. In this study, the efficacy of immunization with immune complexes in overcoming age-associated deficiency in GC response was investigated. We show that the depressed GC response in aged mice can be significantly elevated by immunization with immune complexes. Importantly, there is a significant improvement of B cell memory response and long-lived plasma cells. Our results demonstrate that immune complex immunization may represent a novel strategy to elicit functional GC response in aging, and possibly, to overcome age-related immune deficiency in general.

Objective To investigate the role of CXCL13 in the development and pathogenesis of collagen-induced arthritis (CIA), and to determine the mechanisms involved in the modulation of arthritogenic response by CXCL13 neutralization. Methods Mice were immunized with type II collagen (CII) and treated with anti-CXCL13 or control antibodies during boosting. Mice were monitored for the development and severity of arthritis. The effects of CXCL13 neutralization on immune response to CII were evaluated by cytokine production by CII-specific T cells and CII-specific antibody production. Follicular response in the spleen and in synovial tissue was determined by in situ immunohistology. Results Mice receiving neutralizing antibodies to CXCL13 developed significantly less severe arthritis compared with mice injected with phosphate buffered saline or control antibodies. Follicular response both in the spleen and in synovial tissue was inhibited by anti-CXCL13 treatment. Injection with anti-CXCL13 antibodies did not significantly affect antigen-specific recall lymphocyte proliferation or type 1 cytokine production in vitro. Antibody response specific to CII was not inhibited by anti-CXCL13 treatment. However, anti-CXCL13 treatment induced significantly higher levels of interleukin-10 production after in vitro CII stimulation. Conclusion Neutralization of CXCL13 inhibits the development of CIA and reduces follicular response in both lymphoid and nonlymphoid tissues. These findings may have important implications regarding the pathogenesis and treatment of autoimmune arthritis.

B cells play a pathogenic or regulatory role in many autoimmune diseases through production of autoantibodies, cytokine production, and Ag presentation. However, the mechanisms that regulate these B cell functions under different autoimmune settings remain unclear. In the current study, we found that when B cells overexpress an antiapoptotic gene, BclXL, they significantly increased production of IFN-γ and enhanced Th1 response. Consistently, Bcl-xL transgenic mice developed more severe and sustained collagen-induced arthritis due to the enhanced Th1 response. The production of autoantibodies in BclXL transgenic mice was comparable to that in wild-type mice. Thus, our results indicate a novel role of BclXL in regulating B cell functions and immune responses. In patients with rheumatoid arthritis, arthritogenic B cells often up-regulate BclXL expression, which may not only render B cells resistant to apoptosis but also alter the ability of the autoreactive B cells to produce cytokines and modulate the inflammatory response. This may have therapeutic implications if BclXL expression can be down-regulated in autoreactive B cells.

Objective To study the role of the lymphotoxin (LT) signaling pathway in the development and pathogenesis of collagen-induced arthritis (CIA), and to understand the mechanisms by which blockade of the LT pathway influences the arthritogenic response to type II collagen (CII). Methods LTα-deficient and wild-type C57BL/6 mice were immunized with CII. Male DBA/1 mice were immunized with CII and treated with LTβ receptor immunoglobulin fusion protein (LTβR-Ig) or control Ig. Mice were monitored for the development and severity of arthritis. The effects of LT blockade on immune responses were evaluated by cytokine production and antigen-specific proliferation in vitro, the delayed-type hypersensitivity (DTH) response, and serum levels of CII-specific antibodies. Results CIA that developed in LTα-deficient mice was more severe and prolonged than that which developed in wild-type mice. Blocking LT signaling with LTβR-Ig significantly exacerbated the disease. Exacerbation of CIA was associated with an enhanced Th1-type response, including increased type 1 cytokine production, an enhanced DTH response, and elevated production of CII-specific IgG2a antibodies. Conclusion Blockade of the LT signaling pathway exacerbates the development and progression of CIA, probably by skewing the Th1/Th2 balance that determines the outcome of autoimmune responses.