The majority of HIV infected individuals fail to produce protective antibodies and have diminished responses to immunization1–3. We report that even though there is an expansion of T follicular helper (Tfh) cells in HIV infected individuals, these are unable to provide adequate B cell help. A higher frequency of PD-L1+ germinal center (GC) B cells from lymph nodes of HIV infected individuals suggested a potential role for PD-1/PD-L1 interaction in regulating Tfh cell function. In fact, engagement of PD-1 on Tfh cells led to a reduction in cell proliferation, activation, ICOS expression and IL-21 cytokine secretion. Importantly, blocking PD-1 signaling enhanced HIV-specific immunoglobulin production in vitro. We further show that at least part of this defect involves IL-21 as addition of this cytokine rescued antibody responses and plasma cell generation. Our results suggest that deregulation of Tfh-mediated B cell help diminishes B cell responses during HIV infection and may be related to PD-1 triggering on Tfh cells. These results show, for the first time, a role for Tfh cell function in HIV pathogenesis and suggest that an alteration in their function could have a significant impact on the outcome and control of HIV infection, future infections and vaccinations.
Aging leads to dysregulation of multiple components of the immune system that results in increased susceptibility to infections and poor response to vaccines in the aging population. The dysfunctions of adaptive B and T cells are well documented, but the effect of aging on innate immunity remains incompletely understood. Using a heterogeneous population of peripheral blood mononuclear cells (PBMCs), we first undertook transcriptional profiling and found that PBMCs isolated from old individuals (≥ 65 years) exhibited a delayed and altered response to stimulation with TLR4, TLR7/8, and RIG-I agonists compared to cells obtained from adults (≤ 40 years). This delayed response to innate immune agonists resulted in the reduced production of pro-inflammatory and antiviral cytokines and chemokines including TNFα, IL-6, IL-1β, IFNα, IFNγ, CCL2, and CCL7. While the major monocyte and dendritic cell subsets did not change numerically with aging, activation of specific cell types was altered. PBMCs from old subjects also had a lower frequency of CD40+ monocytes, impaired up-regulation of PD-L1 on monocytes and T cells, and increased expression of PD-L2 and B7-H4 on B cells. The defective immune response to innate agonists adversely affected adaptive immunity as TLR-stimulated PBMCs (minus CD3 T cells) from old subjects elicited significantly lower levels of adult T-cell proliferation than those from adult subjects in an allogeneic mixed lymphocyte reaction (MLR). Collectively, these age-associated changes in cytokine, chemokine and interferon production, as well as co-stimulatory protein expression could contribute to the blunted memory B- and T-cell immune responses to vaccines and infections.
Impaired immune responses in the elderly lead to reduced vaccine efficacy and increased susceptibility to viral infections. Although several groups have documented age-dependent defects in adaptive immune priming, the deficits that occur prior to antigen encounter remain largely unexplored. Herein, we identify novel mechanisms for compromised adaptive immunity that occurs with aging in the context of infection with West Nile virus (WNV), an encephalitic flavivirus that preferentially causes disease in the elderly. An impaired IgM and IgG response and enhanced vulnerability to WNV infection during aging was linked to delayed germinal center formation in the draining lymph node (DLN). Adoptive transfer studies and two-photon intravital microscopy revealed a decreased trafficking capacity of donor naïve CD4+ T cells from old mice, which manifested as impaired T cell diapedesis at high endothelial venules and reduced cell motility within DLN prior to antigen encounter. Furthermore, leukocyte accumulation in the DLN within the first few days of WNV infection or antigen-adjuvant administration was diminished more generally in old mice and associated with a second aging-related defect in local cytokine and chemokine production. Thus, age-dependent cell-intrinsic and environmental defects in the DLN result in delayed immune cell recruitment and antigen recognition. These deficits compromise priming of early adaptive immune responses and likely contribute to the susceptibility of old animals to acute WNV infection.
Age-related alterations in immunity have been linked to increased incidence of infections and decreased responses to vaccines in the aging population. Human peripheral blood monocytes are known to promote antigen presentation and antiviral activities; however, the impact of aging on monocyte functions remains an open question. We present an in-depth global analysis examining the impact of aging on classical (CD14+CD16−), intermediate (CD14+CD16+), and non-classical (CD14dimCD16+) monocytes. Monocytes sorted from non-frail healthy adults (21–40 yrs) and old (≥ 65 yrs) individuals were analyzed after stimulation with TLR4, TLR7/8, and RIG-I agonists. Our data showed under non-stimulated conditions, monocyte subsets did not reveal significant age-related alternations; however, agonist stimulated-monocytes from adults and old subjects did show differences at the transcriptional and functional levels. These alternations in many immune-related transcripts and biological processes resulted in reduced production of IFNα, IFNγ, IL-1β, CCL20, and CCL8, and higher expression of CX3CR1 in monocytes from old subjects. Our findings represent a comprehensive analysis of the influence of human aging on pattern recognition receptors signaling and monocyte functions, and have implications for strategies to enhance the immune response in the context of infection and immunization.
Sindbis virus (SINV) infection of the central nervous system (CNS) provides a model for understanding the role of the immune response in recovery from alphavirus infection of neurons. Virus clearance occurred in three phases: clearance of infectious virus (days 3 to 7), clearance of viral RNA (days 8 to 60), and maintenance of low levels of viral RNA (>day 60). The antiviral immune response was initiated in the cervical lymph nodes with rapid extrafollicular production of plasmablasts secreting IgM, followed by germinal center production of IgG-secreting and memory B cells. Alphaviruses of the family Togaviridae are an important cause of acute mosquito-borne viral encephalomyelitis in the Americas (7, 59). Neurons of the brain and spinal cord are the primary target cells, and recovery requires immune-mediated control of infection in these nonrenewable cells. Virus clearance from neurons poses unique challenges for the immune system. The restriction of the blood-brain barrier to immune effector entry into the central nervous system (CNS), reduced expression of major histocompatibility complex (MHC) classes I and II, and terminal differentiation of neurons make virus clearance more difficult (15). A noncytolytic process is needed to avoid irreversible neurologic damage, and the process must be effective to avoid chronic or progressive neurologic disease. Previous studies of immunodeficient mice infected with Sindbis virus (SINV), the prototype alphavirus, have shown that clearance of infectious virus from neurons within 7 to 8 days is mediated by gamma interferon (IFN-␥) produced by T cells and anti-E2 glycoprotein antibodies (Abs) produced by B cells (4, 23).Although infectious virus is cleared from the CNS to undetectable levels after infection, viral RNA encoding both structural and nonstructural viral proteins can be detected in the brains and spinal cords of SINV-infected BALB/c mice for at least a year after recovery (55,22). In severe combined immunodeficiency (SCID) mice, production of infectious SINV resumes as levels of passively transferred Ab decrease, indicating that persistent RNA is capable of renewed replication (22).Persistence of viral RNA in the CNS suggests the need for long-term immune-mediated suppression of SINV reactivation after the acute phase of infection. Previous studies of BALB/c mice have shown that the acute inflammatory response to SINV infection includes the infiltration of T cells and B cells into the CNS (18,40). Additional studies have shown that B-cell-deficient (MT) C57BL/6 mice are unable to clear infectious virus from cortical and hippocampal neurons and that initial successful SINV clearance from brain stem and spinal cord motor neurons is followed by virus reactivation after 18 to 22 days, demonstrating a critical role for Ab in recovery (4, 6). The presence of SINV-specific Ab-secreting cells (ASCs) in the brains of immunologically normal mice for at least a year after recovery from infection further suggests a role for intrathecal Ab production in the long-term suppres...
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