Isolation and characterization of Leu 7+ germinal-center cells with the T helper-cell phenotype and granular lymphocyte morphology

In Situ Characterization of Follicular Helper CD4 T Cells Using Multiplexed Imaging

Follicular helper CD4 T (Tfh) cells play an essential role in the formation of germinal centers (GCs), where mature B cells proliferate, differentiate, and provide long-term protective humoral responses. Despite the extensive phenotypic characterization and identification of human Tfh cell subsets, their spatial positioning at tissue level is not well understood. Here, we describe a quantitative multiplexed immunofluorescence approach allowing for the comprehensive in situ characterization of Tfh cells in human tonsils and lymph nodes (LNs) from individuals with angioimmunoblastic T-cell lymphoma (AITL). We have developed eight multiplexed panels comprising a spectrum of Tfh cell markers, like PD-1, CXCR5, and ICOS, along with transcription factors (Bcl6, Tbet, GATA3), to assess their expression, frequencies, spatial distribution and co-localization in a quantitative manner. Combined analysis of relevant markers revealed the presence of several Tfh cell subsets at tissue level based on the differential expression of surface receptors, nuclear factors as well as their distinct localization within the follicular areas. Interestingly, we found a considerable amount of tonsillar Tfh cells expressing high levels of the Th2 regulator GATA3. The co-expression of GATA3, CXCR5, and BCL6, points to an important role of GATA3 for the generation of effector human Tfh cells. Furthermore, our data revealed significantly different Tfh cell profile signatures between health and disease. Therefore, our imaging platform generates meaningful information for the in situ characterization of human Tfh cells and could provide the base for future studies aiming to a comprehensive understanding of Tfh cell tissue heterogeneity.

Follicular helper T-cells: expanding roles in T-cell lymphoma and targets for treatment

Follicular helper T-cells (Tfh cells) are a subset of CD4(+) T-cells that are essential for normal production of high affinity antibodies. Tfh cells characteristically produce IL21 and IL4 and show high expression of surface markers CXCR5, ICOS, PDCD1 (PD-1) and the chemokine CXCL13. In this review we will focus on the emerging links between Tfh cells and subtypes of T-cell non-Hodgkin lymphoma: angioimmunoblastic T-cell lymphoma (AITL) and ~20% of peripheral T-cell lymphoma not otherwise specified (PTCL-NOS) have surface marker features of Tfh cells and share a spectrum of genetic abnormalities. The recurrent genetic abnormalities associated with AITL include mutations in epigenetic modifiers such as TET2 and DNMT3A and the motility and adhesion gene, RHOA, is mutated in up to 70% of cases. ~20% of PTCL-NOS demonstrate RHOA mutations and have other characteristics suggesting an origin in Tfh cells. The recognition that specific genetic and surface markers are associated with malignant Tfh cells suggests that the next few years will bring major changes in diagnostic and treatment possibilities. For example, antibodies against IL21, PDCD1 and ICOS are already in clinical trials for autoimmune disease or other malignancies and antibodies against CXCL13 are in pre-clinical development.

T follicular helper (TFH) cells in normal and dysregulated immune responses

T cell help for antibody production is a fundamental aspect of immune responses. Only recently has a better understanding of the cellular and molecular mechanisms for T cell help emerged. A subset of T cells, termed T follicular helper cells (T(FH) cells), provides a helper function to B cells and represents one of the most numerous and important subsets of effector T cells in lymphoid tissues. T(FH) cells are distinguishable from Th1 and Th2 cells by several criteria, including chemokine receptor expression (CXCR5), location/migration (B cell follicles), and function (B cell help). Central to the function of CD4(+) T cells is IL-21, a "helper" cytokine produced by T(FH) cells that potently stimulates the differentiation of B cells into Ab-forming cells through IL-21R. Consequently, dysregulation of T(FH) cell function, and over- or under-expression of T(FH) cell-associated molecules such as ICOS or IL-21, most likely contributes to the pathogenesis of certain autoimmune diseases or immunodeficiencies.

T cells and cytokines in intracellular bacterial infections: experiences with Mycobacterium bovis BCG

Intracellular bacteria reside in mononuclear phagocytes, and protective immunity is dominated by T lymphocytes. Mycobacterium bovis bacillus Calmette-Guéin (BCG) infection of mice represents an excellent model for studying immune mechanisms involved in defence against persistent intracellular bacteria that cause chronic disease. Gene disruption mutant mice include: A beta-/-, which lack conventional CD4+ T cell receptor alpha/beta (TCR alpha/beta) T lymphocytes; beta 2 microglobulin -/-, which lack conventional CD8+ TCR alpha/beta lymphocytes; TCR beta-/-, which lack all TCR alpha/beta lymphocytes; TCR delta-/-, which lack all TCR gamma/delta lymphocytes; and RAG-1-/- mutants, which lack mature T and B lymphocytes. Studies of these mutants suggest that CD4+ TCR alpha/beta, CD8+ TCR alpha/beta and TCR gamma/delta T lymphocytes all contribute to immunity against M. bovis BCG. Activation of antibacterial effector functions in macrophages by T helper 1 (Th1) cell-derived gamma-interferon (IFN-gamma) is central to protection. In contrast, Th2 cells are only marginally involved. Activation of Th1 and Th2 cells is regulated by interleukin 10 (IL-10) and IL-12, which are induced early in infection with M. bovis BCG. Although IL-12 is stimulated by M. bovis BCG in immunocompetent mice, studies with IFN-gamma receptor-deficient and tumour necrosis factor alpha (TNF-alpha) receptor-deficient mutant mice suggest that M. bovis BCG-induced IL-12 secretion depends on IFN-gamma and TNF-alpha. Hence, IL-12 cannot be the first cytokine produced during M. bovis BCG infection.

Human CD57+ germinal center-T cells are the major helpers for GC-B cells and induce class switch recombination

Background

The function of CD57⁺ CD4⁺ T cells, constituting a major subset of germinal center T (GC-Th) cells in human lymphoid tissues, has been unclear. There have been contradictory reports regarding the B cell helping function of CD57⁺ GC-Th cells in production of immunoglobulin (Ig). Furthermore, the cytokine and co-stimulation requirement for their helper activity remains largely unknown. To clarify and gain more insight into their function in helping B cells, we systematically investigated the capacity of human tonsil CD57⁺ GC-Th cells in inducing B cell Ig synthesis.

Results

We demonstrated that CD57⁺ GC-Th cells are highly efficient in helping B cell production of all four subsets of Ig (IgM, IgG, IgA and IgE) compared to other T-helper cells located in germinal centers or interfollicular areas. CD57⁺ GC-Th cells were particularly more efficient than other T cells in helping GC-B cells but not naïve B cells. CD57⁺ GC-Th cells induced the expression of activation-induced cytosine deaminase (AID) and class switch recombination in developing B cells. IgG1-3 and IgA1 were the major Ig isotypes induced by CD57⁺ GC-Th cells. CD40L, but not IL-4, IL-10 and IFN-γ, was critical in CD57⁺ GC-Th cell-driven B cell production of Ig. However, IL-10, when added exogenously, significantly enhanced the helper activity of CD57⁺ GC-Th cells, while TGF-β1 completely and IFN-γ partially suppressed the CD57⁺ GC-Th cell-driven Ig production.

Conclusions

CD57⁺CD4⁺ T cells in the germinal centers of human lymphoid tissues are the major T helper cell subset for GC-B cells in Ig synthesis. Their helper activity is consistent with their capacity to induce AID and class switch recombination, and can be regulated by CD40L, IL-4, IL-10 and TGF-β.

Subspecialization of CXCR5+ T cells: B helper activity is focused in a germinal center-localized subset of CXCR5+ T cells

The T helper (Th) cell pool is composed of specialized cells with heterogeneous effector functions. Apart from Th1 and 2 cells, CXCR5+ T cells have been suggested to be another type of effector T cell specialized for B cell help. We show here that CXCR5+ T cells are heterogeneous, and we identify subsets of CXCR5+ CD4 T cells that differ in function and microenvironmental localization in secondary lymphoid tissues. CD57+CXCR5 T cells, hereafter termed germinal center Th (GC-Th) cells, are localized only in GCs, lack CCR7, and are highly responsive to the follicular chemokine B lymphocyte chemoattractant but not to the T cell zone EBI1-ligand chemokine. Importantly, GC-Th cells are much more efficient than CD57-CXCR5+ T cells or CXCR5- T cells in inducing antibody production from B cells. Consistent with their function, GC-Th cells produce elevated levels of interleukin 10 upon stimulation which, with other cytokines and costimulatory molecules, may help confer their B cell helper activity. Our results demonstrate that CXCR5+ T cells are functionally heterogeneous and that the GC-Th cells, a small subset of CXCR5+ T cells, are the key helpers for B cell differentiation and antibody production in lymphoid tissues.

The unenlarged lymph nodes of HIV-1-infected, asymptomatic patients with high CD4 T cell counts are sites for virus replication and CD4 T cell proliferation. The impact of highly active antiretroviral therapy

The efficacy of triple drug therapy for HIV-1 infection encourages its early use to prevent damage to the immune system. We monitored the effects of such therapy on 12 patients with 14-75-mo histories of minimal disease, i.e., CD4+ counts constantly >500/microl and little or no lymph node enlargement. In this way, we could first determine the extent of viral replication and immunoarchitectural changes in unenlarged nodes early in disease, and second follow the response to triple therapy in plasma and lymphoid tissue in tandem. As is known for lymph nodes with more advanced disease, the germinal centers showed productively infected T cells, i.e., CD4+CD1a-CD68- cells labeling intensely for HIV-1 RNA after in situ hybridization. The unenlarged nodes also showed extensive HIV-1 RNA retention on a well-preserved, follicular dendritic cell (FDC) network, and the follicles were abnormal. There were numerous CD8+ cells, many expressing TIA-1 granule antigen. Also, in contrast to normal follicles, CD4+ T cell proliferation was active, with marked increases in the number of cycling, Ki-67+CD4+CD45R0+ cells. After 28 d and 3 mo of therapy, productively infected T cells decreased dramatically and often were not apparent. The labeling of the FDC network for viral RNA also decreased, but not for gag protein. We conclude that HIV-1 replicates and accumulates in lymphoid organs before damage of the immune system, that at this stage of disease de novo production of T cells occurs in the lymphoid tissue, and that the infection is sensitive to triple drug therapy in both plasma and lymph nodes.

Phenotype of Hodgkin and Sternberg-Reed cells and expression of CD57 (LEU7) antigen

Possible associations between the immunophenotype of Hodgkin (H) and Sternberg-Reed (S-R) cells, the expression of CD57 (Leu 7) antigen, and the presence of Epstein-Barr virus (EBV) were investigated in lymph node specimens from 50 cases of Hodgkin's disease (HD), including 26 cases of mixed cellularity and 24 cases of nodular sclerosis. Tissues were fixed in 10% neutral formalin, or/and B5 solution. H and S-R cells were CD30+, CD15+ (85% of the cases) and LCA (CD45). A proportion of neoplastic cells positive for either T-cell markers (CD3) or B-cell markers (CD20) was observed in 10% and 34% of the cases, respectively. Membrane positivity for CD57 antigen was found in H and S-R cells in 10 cases (8 cases of mixed cellularity, and 2 cases of nodular sclerosis). Such immunopositivity was only observed in B5-fixed sections. No staining for CD57 antigen was identified in H and S-R cells of any case with CD20 positive neoplastic cells. H and S-R cells of both CD57-positive and CD57-negative cases were further studied by immunohistochemistry for LMP1, by in-situ hybridization for EBER and by polymerase chain reaction (PCR) for EBV-DNA. No association was identified between the expression of CD57 antigen and the presence of EBV sequences, transcripts or proteins. Our findings do not support a B-cell origin for H and S-R cells in CD57-positive cases of Hodgkin's disease and suggest that these neoplastic cells may be related to natural killer (NK) or T-cells expressing CD57 antigen.

T-cell chronic lymphocytic leukemia. Unusual morphologic, phenotypic, and karyotypic features in association with light chain amyloidosis

BACKGROUND

Lymphocytes that display a phenotype of mature B-cells, T-cells, natural killer (NK) cells, or a combination of T-cells and NK cells can be found in patients with lymphoproliferations that manifest as expansions of peripheral blood lymphocytes (PBL). If these PBL expansions exhibit clonality, they can be classified as chronic lymphocytic leukemia (CLL).

METHODS/RESULTS

A patient who had two simultaneous, clonal lymphoproliferative disorders manifested as an unusual T-cell CLL in conjunction with systemic light chain amyloidosis is described. Gene rearrangement studies of the PBL of the patient showed clonal rearrangements of both the T-cell receptor beta (T beta) chain and the immunoglobulin genes. Additional immunologic and microscopic studies of the T-cells of the patient showed that they were large, agranular, CD4+ T-cells that also expressed the NK cell marker CD57. Cytogenetics disclosed an unusual karyotype in the PBL.

CONCLUSIONS

The pathogenesis of this T-cell CLL and whether it truly represents a malignant disorder, as well as its relation to amyloidosis, is discussed.

Mice lacking MHC class II molecules

We have produced mice that lack major histocompatibility complex class II antigens, permitting us to evaluate the role of these molecules in diverse aspects of T and B cell differentiation. The mutant mice show near-complete elimination of CD4+ T lymphocytes from the spleen and lymph nodes; the few remaining CD4-positive cells are preferentially localized to B cell follicles. Surprisingly, substantial numbers of CD4 single-positive cells reside in the thymus; however, these are not mature thymocytes as we currently recognize them. B lymphocytes occur in normal numbers and are capable of terminal differentiation to plasma cells. Nevertheless, several aberrations in the B cell compartment are demonstrable: a lack of germinal centers, fewer IgM+IgD+ cells in certain individuals, reduced production of serum IgG1, and complete inability to respond to T-dependent antigens. In short, the class II-negative mice have confirmed some old ideas about lymphocyte differentiation, but have provided some surprises.

Correlation between cytomegalovirus and toxoplasma gondii serology and lymphocyte phenotypes in peripheral blood and cord blood

Increased numbers of peripheral blood HNK1+ lymphocytes have been reported in transplant recipients, hemophilia patients treated with clotting factor concentrates, and HIV carriers. Our previous work has revealed a significant effect of cytomegalovirus (CMV) carrier status on HNK1+ lymphocytes. Since other antigenic stimuli may be also involved, we compared the effects of Toxoplasma gondii and CMV carrier status on lymphocyte subsets as defined by the CD3 and HNK1 markers in 288 healthy individuals. In contrast to CMV, T gondii carrier status had no significant effects on the CD3+, HNK1+ and CD3-, HNK1+ lymphocyte subsets. That result may be explained by the different relationships between these 2 microorganisms and their hosts. We also studied the effect of maternal CMV carrier status on the HNK1 expression by their offsprings' cord blood lymphocytes. None of the 100 newborns studied had serological evidence of congenital CMV infection. There were only few HNK1+ lymphocytes in the cord bloods, of which the majority was CD3-, and their proportions were not significantly influenced by maternal CMV carrier status. Since there has been probably no direct contact between maternal CMV and the newborns' immune systems, we suggest that the effect of CMV on the HNK1+ lymphocytes of its carriers, results from a direct interaction between virus or virus-infected cells and the immune system.

Increased number of CD4 cells able to bind to natural killer cell targets in the peripheral blood of AIDS related complex patients

CD4 cells forming conjugates with natural killer target cells (K562 cells) were measured in the peripheral blood of anti-HIV antibody positive AIDS related complex (ARC) patients and in three control groups (asymptomatic individuals at risk, normal healthy people and patients with acute hepatitis B). These CD4 cells, which are unable to kill K562 cells, were significantly increased in ARC patients as compared to the control groups. Our data indicate that classical CD4 cells are partially replaced, in ARC patients, by a population of natural killer-target binding granular CD4 lymphocytes, and suggest that the functional abnormalities of helper T cells in these patients may be in part a consequence of the relative predominance of these non IL-2 and BCGF producing cells within the circulating CD4 population.