T-cell-mediated activation of B cells

Prediagnostic serum sCD27 and sCD30 in serial samples and risks of non-Hodgkin lymphoma subtypes

Elevated prediagnostic serum levels of the immune activation markers sCD27 and sCD30 have been associated with non-Hodgkin lymphoma (NHL). However, the use of a single sample per participant in these studies has limited etiologic inferences. We report findings, overall and by NHL subtype, from a case-control analysis (422 cases, 434 controls) within the Janus Serum Bank with two samples per subject collected on average 5 years apart. Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) was associated with elevated sCD27 in the later, but not earlier, prediagnostic sample (odds ratio [OR] 4.2, 95% confidence interval [CI] 1.5-11.6 and 1.7, 0.7-4.7 per log increase, respectively) in analyses adjusting for both analytes, while follicular lymphoma (FL) was associated with elevated sCD30 in both the later and earlier samples (OR 2.9, 95% CI 1.4-4.4 and 2.3, 1.2-4.4, respectively). CLL/SLL cases were significantly more likely than controls to have higher sCD27 in the later vs. earlier sample (OR 1.4, 95% CI 1.1-1.9 per standard deviation increase); no such difference in sCD30 was apparent for FL. In a joint analysis, NHL cases were more likely than controls to have below-median sCD27 in the earlier sample and above-median sCD27 in the later sample (OR 1.5, 95% CI 1.0-2.3). For sCD30, the association between sCD30 and FL was confined to subjects with above-median analyte levels in both samples (OR 2.5, 95% CI 1.1-5.9). Our findings are compatible with elevated sCD27 representing a disease-induced effect and sCD30 representing a marker of increased FL susceptibility.

Single-cell tracking of flavivirus RNA uncovers species-specific interactions with the immune system dictating disease outcome

Positive-sense RNA viruses pose increasing health and economic concerns worldwide. Our limited understanding of how these viruses interact with their host and how these processes lead to virulence and disease seriously hampers the development of anti-viral strategies. Here, we demonstrate the tracking of (+) and (−) sense viral RNA at single-cell resolution within complex subsets of the human and murine immune system in different mouse models. Our results provide insights into how a prototypic flavivirus, yellow fever virus (YFV-17D), differentially interacts with murine and human hematopoietic cells in these mouse models and how these dynamics influence distinct outcomes of infection. We detect (−) YFV-17D RNA in specific secondary lymphoid compartments and cell subsets not previously recognized as permissive for YFV replication, and we highlight potential virus–host interaction events that could be pivotal in regulating flavivirus virulence and attenuation.

Analysis of virus replication on a single-cell level is often hampered by a lack of specific or sensitive enough reagents. Here, Douam et al. use RNA-flow technique to track (+) and (−) strand RNA of yellow fever virus in hematopoietic cells in mouse models and identify virus-host interactions that affect disease outcome.

Increasing JAK/STAT Signaling Function of Infant CD4+ T Cells during the First Year of Life

Most infant deaths occur in the first year of life. Yet, our knowledge of immune development during this period is scarce and derived from cord blood (CB) only. To more effectively combat pediatric diseases, a deeper understanding of the kinetics and the factors that regulate the maturation of immune functions in early life is needed. Increased disease susceptibility of infants is generally attributed to T helper 2-biased immune responses. The differentiation of CD4+ T cells along a specific T helper cell lineage is dependent on the pathogen type, and on costimulatory and cytokine signals provided by antigen-presenting cells. Cytokines also regulate many other aspects of the host immune response. Therefore, toward the goal of increasing our knowledge of early immune development, we defined the temporal development of the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling function of CD4+ T cells using cross-sectional blood samples from healthy infants ages 0 (birth) to 14 months. We specifically focused on cytokines important in T cell differentiation (IFN-γ, IL-12, and IL-4) or in T cell survival and expansion (IL-2 and IL-7) in infant CD4+ T cells. Independent of the cytokine tested, JAK/STAT signaling in infant compared to adult CD4+ T cells was impaired at birth, but increased during the first year, with the most pronounced changes occurring in the first 6 months. The relative change in JAK/STAT signaling of infant CD4+ T cells with age was distinct for each cytokine tested. Thus, while about 60% of CB CD4+ T cells could efficiently activate STAT6 in response to IL-4, less than 5% of CB CD4+ T cells were able to activate the JAK/STAT pathway in response to IFN-γ, IL-12 or IL-2. By 4-6 months of age, the activation of the cytokine-specific STAT molecules was comparable to adults in response to IL-4 and IFN-γ, while IL-2- and IL-12-induced STAT activation remained below adult levels even at 1 year. These results suggest that common developmental and cytokine-specific factors regulate the maturation of the JAK/STAT signaling function in CD4+ T cells during the first year of life.

Acquisition of host-derived CD40L by HIV-1 in vivo and its functional consequences in the B-cell compartment

Aberrant activation of the B-cell compartment and hypergammaglobulinemia were among the first recognized characteristics of HIV-1-infected patients in the early 1980s. It has been demonstrated previously that HIV-1 particles acquire the costimulatory molecule CD40L when budding from activated CD4(+) T cells. In this paper, we confirmed first that CD40L-bearing virions are detected in the plasma from untreated HIV-1-infected individuals. To define the biological functions of virus-associated CD40L and fully characterize its influence on the activation state of B cells, we conducted a large-scale gene expression analysis using microarray technology on B cells isolated from human tonsillar tissue. Comparative analyses of gene expression profiles revealed that CD40L-bearing virions induce a highly similar response to the one observed in samples treated with a CD40 agonist, indicating that virions bearing CD40L can efficiently activate B cells. Among modulated genes, many cytokines/chemokines (CCL17, CCL22), surface molecules (CD23, CD80, ICAM-1), members of the TNF superfamily (FAS, A20, TNIP1, CD40, lymphotoxin alpha, lymphotoxin beta), transcription factors and associated proteins (NFKB1, NFKBIA, NFKBIE), second messengers involved in CD40 signaling (TRAF1, TRAF3, MAP2K1, phosphatidylinositol 3-kinase), and the activation-induced cytidine deaminase (AID) were identified. Moreover, we show that soluble factors induced upon the exposure of B cells to CD40L-bearing virions can exert chemoattractant properties toward CD4(+) T cells. We thus propose that a positive feedback loop involving CD40L-bearing HIV-1 particles issued from CD4(+) T cells productively infected with HIV-1 play a role in the virus-induced dysfunction of humoral immunity by chronically activating B cells through sustained CD40 signaling.

K+ channel expression during B cell differentiation: implications for immunomodulation and autoimmunity

Using whole-cell patch-clamp, fluorescence microscopy and flow cytometry, we demonstrate a switch in potassium channel expression during differentiation of human B cells from naive to memory cells. Naive and IgD(+)CD27(+) memory B cells express small numbers of the voltage-gated Kv1.3 and the Ca(2+)-activated intermediate-conductance IKCa1 channel when quiescent, and increase IKCa1 expression 45-fold upon activation with no change in Kv1.3 levels. In contrast, quiescent class-switched memory B cells express high levels of Kv1.3 ( approximately 2000 channels/cell) and maintain their Kv1.3(high) expression after activation. Consistent with their channel phenotypes, proliferation of naive and IgD(+)CD27(+) memory B cells is suppressed by the specific IKCa1 inhibitor TRAM-34 but not by the potent Kv1.3 blocker Stichodactyla helianthus toxin, whereas the proliferation of class-switched memory B cells is suppressed by Stichodactyla helianthus toxin but not TRAM-34. These changes parallel those reported for T cells. Therefore, specific Kv1.3 and IKCa1 inhibitors may have use in therapeutic manipulation of selective lymphocyte subsets in immunological disorders.

Localization of recombination activating gene 1/green fluorescent protein (RAG1/GFP) expression in secondary lymphoid organs after immunization with T-dependent antigens in rag1/gfp knockin mice

Secondary rearrangements of immunoglobulin gene segments that generate a new antibody repertoire in peripheral B cells have been described as receptor revision and occur by as yet unknown mechanisms. To determine the importance of recombination activating gene (RAG) expression in receptor revision, heterozygous rag1/green fluorescent protein (gfp) knockin mice were used to examine the location of RAG1 expression in the germinal centers (GCs) of lymphoid follicles after immunization with a variety of T-cell-dependent antigens. Immunization of rag1/gfp heterozygous mice or rag1 homozygous knockout mice reconstituted with rag1/gfp heterozygous spleen cells caused the down-regulation of RAG1/GFP signal in GCs. Although some RAG1/GFP(+) cells appeared in regions surrounding the peanut agglutinin (PNA)(+)GL-7(+) GC area, RAG1/GFP(+) cells did not accumulate in the central region. In addition, the stimulation of spleen B cells with anti-mu antibody plus interleukin-4 (IL-4) or with anti-CD40 monoclonal antibody plus IL-7 did not induce GFP signals at detectable levels in vitro. These results clearly demonstrate that RAG1 re-expression either does not occur or is at extremely low levels in antigen-driven B cells in GCs of secondary lymphoid follicles, suggesting that other mechanisms may mediate the gene rearrangements observed in receptor revision.