Auto- and polyreactivity of IgM from CD5+ and CD5- cord blood B cells

Post-transcriptional (re)programming of B lymphocyte development: From bench to bedside?

Hematopoiesis, a process which generates blood and immune cells, changes significantly during mammalian development. Definitive hematopoiesis is marked by the emergence of long-term hematopoietic stem cells (HSCs). Here, we will focus on the post-transcriptional differences between fetal liver (FL) and adult bone marrow (ABM) HSCs. It remains unclear how or why exactly FL HSCs transition to ABM HSCs, but we aim to leverage their differences to revive an old idea: in utero HSC transplantation. Unexpectedly, the expression of certain RNA-binding proteins (RBPs) play an important role in HSC specification, and can be employed to convert or reprogram adult HSCs back to a fetal-like state. Among other features, FL HSCs have a broad differentiation capacity that includes the ability to regenerate both conventional B and T cells, as well as innate-like or unconventional lymphocytes such as B-1a and marginal zone B (MzB) cells. This chapter will focus on RNA binding proteins, namely LIN28B and IGF2BP3, that are expressed during fetal life and how they promote B-1a cell development. Furthermore, this chapter considers a potential clinical application of synthetic co-expression of LIN28B and IGF2BP3 in HSCs.

Neonatal Rhesus Macaques Have Distinct Immune Cell Transcriptional Profiles following HIV Envelope Immunization

HIV-1-infected infants develop broadly neutralizing antibodies (bnAbs) more rapidly than adults, suggesting differences in the neonatal versus adult responses to the HIV-1 envelope (Env). Here, trimeric forms of HIV-1 Env immunogens elicit increased gp120- and gp41-specific antibodies more rapidly in neonatal macaques than adult macaques. Transcriptome analyses of neonatal versus adult immune cells after Env vaccination reveal that neonatal macaques have higher levels of the apoptosis regulator BCL2 in T cells and lower levels of the immunosuppressive interleukin-10 (IL-10) receptor alpha (IL10RA) mRNA transcripts in T cells, B cells, natural killer (NK) cells, and monocytes. In addition, immunized neonatal macaques exhibit increased frequencies of activated blood T follicular helper-like (Tfh) cells compared to adults. Thus, neonatal macaques have transcriptome signatures of decreased immunosuppression and apoptosis compared with adult macaques, providing an immune landscape conducive to early-life immunization prior to sexual debut.

Cross-reactivity of HIV vaccine responses and the microbiome

PURPOSE OF REVIEW

A successful human immunodeficiency virus-type 1 (HIV-1) vaccine will require immunogens that induce protective immune responses. However, recent studies suggest that the response to HIV-1 and perhaps other viruses may be altered by immune system exposure to intestinal microbiota-antigens. This review will discuss select aspects of these studies.

RECENT FINDINGS

Naïve CD4 T and B cell repertoires can be imprinted by intestinal microbiota-antigens to respond to virus epitopes prior to virus infection. A multiclade envelope (Env) gp145 DNA prime, recombinant adenovirus type 5 boost vaccine tested in a HIV Vaccine Trials Network (HVTN) phase IIb human vaccine efficacy trial (HVTN 505) induced a dominant gp41-reactive antibody response that was non-neutralizing and cross-reactive with intestinal microbiota. This vaccine regimen also induced a dominant gp41-reactive, intestinal microbiota-cross-reactive gp41 antibody response in neonatal and adult Rhesus macaques. Studies of naïve CD4 T cells have demonstrated cross-reactivity to both HIV-1 and influenza peptides.

SUMMARY

HIV-1 Env vaccine-induced CD4 T and B cell responses can originate from a pool of intestinal microbiota-cross-reactive immune cells. Moreover, intestinal microbiota-cross-reactive HIV-1 Env antibodies are ineffective in protection against HIV-1 infection. Thus, intestinal microbiota-imprinting of the B cell repertoire may be one of several roadblocks to the induction of protective HIV-1 antibodies.

Autopolyreactivity Confers a Holistic Role in the Immune System

In this review, we summarize and discuss some key findings from the study of naturally occurring autoantibodies. The B-cell compartment of the immune system appears to recognize almost all endogenous and environmental antigens. This ability is accomplished principally through autopolyreactive humoral and cellular immune receptors. This extended autopolyreactivity (1) along immunoglobulin gene recombination contributes to the immune system's ability to recognize a very large number of self and non-self constituents; and (2) generates a vast immune network that creates communication channels between the organism's interior and exterior. Thus, the immune system continuously evolves depending on the internal and external stimuli it encounters. Furthermore, this far-reaching network's existence implies activities resembling those of classical biological factors or activities that modulate the function of other classical biological factors. A few such antibodies have already been found. Another important concept is that natural autoantibodies are highly dependent on the presence or absence of commensal microbes in the organism. These results are in line with past and recent findings showing the fundamental influence of the microbiota on proper immune system development, and necessitate the existence of a host-microbe homeostasis. This homeostasis requires that the participating humoral and cellular receptors are able to recognize self-antigens and commensal microbes without damaging them. Autopolyreactive immune receptors expressing low affinity for both types of antigens fulfil this role. The immune system appears to play a holistic role similar to that of the nervous system.

Anti-Pneumococcal Capsular Polysaccharide Antibody Response and CD5 B Lymphocyte Subsets

The role of CD19(+) CD5(+) and CD19(+) CD5(-) B cell subpopulations in the antibody response to pneumococcal capsular polysaccharides (caps-PSs) is controversial. In the present study, we evaluated the role of human CD19(+) CD5(+) and CD19(+) CD5(-) cell populations in the serotype-specific antibody response to caps-PS. After vaccination of 5 healthy human adults with Pneumovax (23-valent pneumococcal polysaccharide vaccine [PPV23]), IgG anti-caps-PS serotype 4 antibody-producing cells resided mainly in the CD19(+) CD5(-) B cell subset, as assessed by enzyme-linked immunosorbent spot (ELISpot) analysis. Moreover, in a humanized SCID mouse model, CD19(+) CD5(-) B cells were more effective than CD19(+) CD5(+) cells in producing IgG anti-cap-PS antibodies. Finally, an association was found between the level of IgG anti-caps-PS antibodies and the number of CD19(+) CD5(-) B cells in 33 humans vaccinated with PPV23. Taken together, our data suggest that CD5 defines a functionally distinct population of B cells in humans in the anti-caps-PS immune response.

Analysis of ancestral and functionally relevant CD5 variants in systemic lupus erythematosus patients

Objective

CD5 plays a crucial role in autoimmunity and is a well-established genetic risk factor of developing RA. Recently, evidence of positive selection has been provided for the CD5 Pro224-Val471 haplotype in East Asian populations. The aim of the present work was to further analyze the functional relevance of non-synonymous CD5 polymorphisms conforming the ancestral and the newly derived haplotypes (Pro224-Ala471 and Pro224-Val471, respectively) as well as to investigate the potential role of CD5 on the development of SLE and/or SLE nephritis.

Methods

The CD5 SNPs rs2241002 (C/T; Pro224Leu) and rs2229177 (C/T; Ala471Val) were genotyped using TaqMan allelic discrimination assays in a total of 1,324 controls and 681 SLE patients of Spanish origin. In vitro analysis of CD3-mediated T cell proliferative and cytokine response profiles of healthy volunteers homozygous for the above mentioned CD5 haplotypes were also analyzed.

Results

T-cell proliferation and cytokine release were significantly increased showing a bias towards to a Th2 profile after CD3 cross-linking of peripheral mononuclear cells from healthy individuals homozygous for the ancestral Pro224-Ala471 (CC) haplotype, compared to the more recently derived Pro224-Val471 (CT). The same allelic combination was statistically associated with Lupus nephritis.

Conclusion

The ancestral Ala471 CD5 allele confers lymphocyte hyper-responsiveness to TCR/CD3 cross-linking and is associated with nephritis in SLE patients.

High proportion of CD5+ B cells in infants predicts development of allergic disease

Delayed maturation of the immune system has been proposed to be a risk factor for development of allergy, but B cell maturation in relation to allergic disease has not been examined. B cells lose CD5 and acquire CD27 during maturation from immature via mature/naive to Ig-secreting cells and memory cells. We sought to investigate B cell maturation in relation to development of allergic disease and sensitization in the FARMFLORA birth cohort including 65 Swedish children. Total B cell numbers, proportions of CD5(+) and CD27(+) B cells, and levels of IgM, IgG, IgA, and IgE were measured in blood on repeated occasions from birth to 36 mo of age, and related to allergic disease and sensitization at 18 and 36 mo of age with multivariate discriminant analysis. We also compared the expression of CD24 and CD38 within CD5(+) and CD5(neg) B cells in children and in adults. We found that infants with a high proportion of CD5(+) B cells at birth and at 1 mo of age had an increased risk for having allergic disease at 18 and 36 mo of life. Further, the proportions of CD5(+) B cells at 1 mo of age were inversely correlated with total IgG levels at 18 and 36 mo of age. The majority of the CD5(+) B cells were of a CD24(hi/+)CD38(hi/+) immature/naive phenotype at birth (97%), 7 y of age (95%), and in adults (86%). These results suggest that development of allergic disease is preceded by an immaturity in neonatal B cell phenotype.

Immunophenotyping of putative human B1 B cells in healthy controls and common variable immunodeficiency (CVID) patients

B1 B cells represent a unique subset of B lymphocytes distinct from conventional B2 B cells, and are important in the production of natural antibodies. A potential human homologue of murine B1 cells was defined recently as a CD20(+) CD27(+) CD43(+) cell. Common variable immunodeficiency (CVID) is a group of heterogeneous conditions linked by symptomatic primary antibody failure. In this preliminary report, we examined the potential clinical utility of introducing CD20(+) CD27(+) CD43(+) B1 cell immunophenotyping as a routine assay in a diagnostic clinical laboratory. Using a whole blood assay, putative B1 B cells in healthy controls and in CVID patients were measured. Peripheral blood from 33 healthy donors and 16 CVID patients were stained with relevant monoclonal antibodies and underwent flow cytometric evaluation. We established a rapid, whole blood flow cytometric assay to investigate putative human B1 B cells. Examination of CD20(+) CD27(+) CD43(+) cells is complicated by CD3(+) CD27(+) CD43(hi) T cell contamination, even when using stringent CD20 gating. These can be excluded by gating on CD27(+) CD43(lo-int) B cells. Although proportions of CD20(+)CD27(+)CD43(lo–int) cells within B cells in CVID patients were decreased by 50% compared to controls (P < 0·01), this was not significant when measured as a percentage of all CD27(+) B cells (P = 0·78) [corrected]. Immunophenotypic overlap of this subset with other innate-like B cells described recently in humans is limited. We have shown that putative B1 B cell immunophenotyping can be performed rapidly and reliably using whole blood. CD20(+) CD27(+) CD43(lo-int) cells may represent a distinct B1 cell subset within CD27(+) B cells. CVID patients were not significantly different from healthy controls when existing CD27(+) B cell deficiencies were taken into account.

Infant B cell memory differentiation and early gut bacterial colonization

Germ-free animal models have demonstrated that commensal bacterial colonization of the intestine induces B cell differentiation and activation. Whether colonization with particular bacterial species or groups is associated with B cell development during early childhood is not known. In a prospective newborn/infant cohort including 65 Swedish children, we examined the numbers and proportions of CD20(+), CD5(+), and CD27(+) B cells in blood samples obtained at several time points during the first 3 y of life using flow cytometry. Fecal samples were collected and cultured quantitatively for major facultative and anaerobic bacteria at 1, 2, 4, and 8 wk of life. We found that the numbers of CD20(+) B cells and CD5(+)CD20(+) B cells reached their highest levels at 4 mo, whereas CD20(+) B cells expressing the memory marker CD27 were most numerous at 18 and 36 mo of age. Using multivariate analysis, we show that early colonization with Escherichia coli and bifidobacteria were associated with higher numbers of CD20(+) B cells that expressed the memory marker CD27 at 4 and 18 mo of age. In contrast, we were unable to demonstrate any relation between bacterial colonization pattern and numbers of CD20(+) or CD5(+)CD20(+) B cells. These results suggest that the intestinal bacterial colonization pattern may affect the B cell maturation also in humans, and that an early gut microbiota including E. coli and bifidobacteria might promote this maturation.

Phenotype and function of CD25-expressing B lymphocytes isolated from human umbilical cord blood

BACKGROUND

We have shown that approximately 30% of human peripheral blood B-cells express CD25. B cells expressing CD25 display a mature phenotype belonging to the memory B-cell population and have a better proliferative and antigen-presenting capacity. The aim of the present study was to characterize the CD25-expressing subset of B cells in human cord blood.

MATERIAL AND METHODS

Mononuclear cell fraction from human cord blood (n=34) and peripheral adult blood (n=22) was sorted into CD20+CD25+ and CD20+CD25- B-cell populations. Phenotype and function of these B-cell populations were compared using flow cytometry, proliferation, cytokine production, and immunoglobulin secretion.

RESULTS

CD25-expressing B cells are a limited population of cord blood mononuclear cells representing 5% of the CD20+ B cells. They are characterised by high expression of CD5 in cord blood and CD27 in adult blood. CD25-expressing B cells express a functional IL-2 receptor and high levels of CC-chemokine receptors and spontaneously produce antibodies of IgG and IgM subclass.

CONCLUSIONS

CD25 expression is a common denominator of a specific immunomodulatory B-cell subset ready to proliferate upon IL-2 stimulation, possibly ready to migrate and home into the peripheral tissue for further differentiation/action.

Human B1 cells in umbilical cord and adult peripheral blood express the novel phenotype CD20+ CD27+ CD43+ CD70-

Human B1 cells consist of CD20⁺CD27⁺CD43⁺CD70⁻ cells bearing a skewed B cell receptor repertoire, and are present in umbilical cord and adult peripheral blood.

B1 cells differ in many ways from conventional B cells, most prominently in the production of natural immunoglobulin, which is vitally important for protection against pathogens. B1 cells have also been implicated in the pathogenesis of autoimmune dyscrasias and malignant diseases. It has been impossible to accurately study B1 cells during health and illness because the nature of human B1 cells has not been successfully defined. This has produced controversy regarding the existence of human B1 cells. Here, we determined the phenotype of human B1 cells by testing sort-purified B cell fractions for three fundamental B1 cell functions based on mouse studies: spontaneous IgM secretion, efficient T cell stimulation, and tonic intracellular signaling. We found that a small population of CD20⁺CD27⁺CD43⁺ cells present in both umbilical cord and adult peripheral blood fulfilled these criteria and expressed a skewed B cell receptor repertoire. These B cells express little or no surface CD69 and CD70, both of which are markedly up-regulated after activation of CD20⁺CD27⁻CD43⁻ (naive) and CD20⁺CD27⁺CD43⁻ (memory) B cells. This work identifies human B1 cells as CD20⁺CD27⁺CD43⁺CD70⁻. We determined that the proportion of B1 cells declines with age, which may contribute to disease susceptibility. Identification of human B1 cells provides a foundation for future studies on the nature and role of these cells in human disease.

Rheumatoid factor on a daily basis

Rheumatoid factors (RF), which are antibodies (Ab) with specificity directed against gamma (?) globulins, are the commonest auto-Ab ever described in man. Some of them are referred to as agglutinating RF, others designated non-agglutinating RF. Not only do these characterize rheumatoid arthritis (RA), but they are also encountered in a variety of disease conditions, as well as a proportion of healthy controls. Although non-specific for RA, the measurement of agglutinating IgM-RF remains the most useful serological test for the diagnosis of this disease. Demonstration of abnormal amount of serum RF by any method for which the result has been positive in less than 5% of normal subjects has indeed become one of the seven revised criteria, listed by the American College of Rheumatology (Arnett, FC, Edworthy, SM, Bloch, DA, McShane, DJ, Fries, JF, Cooper, NS, et al. The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis. Arthritis Rheum, 1988: 31: 315-24), for the classification of RA. Over the course of years, the relative importance of genetic (Carson, DA, Chen, PP, Kipps, TJ, Radoux, V, Jirik, FR, Goldfien, RD, et al. Idiotypic and genetic studies of human rheumatoid factors. Arthritis Rheum, 1987: 30: 1321-1325) and environmental (Nemazee, DA, Sato, VL. Enhancing antibody, a novel component of the immune response. Proc Natl Acad Sci USA, 1982: 79: 3828-3832) factors in the production of such intriguing auto-Ab has been delineated.

The kappa gene repertoire of human neonatal B cells

The kappa chain repertoire of individual IgD(+) human neonatal B cells was analyzed using a single cell PCR technique. A total of 104 productive and 90 non-productive VkappaJkappa rearrangements from three cord blood B cell samples were sequenced and compared to the adult IgM(+) peripheral B cell VkappaJkappa repertoire. All six Vkappa families were present in neonatal B cells, but the distribution was not random. In the non-productive repertoire Vkappa2 and Vkappa6 families were less frequent, Vkappa1 and Vkappa3 families were as frequent, and Vkappa4 and Vkappa5 families were more frequent than expected from random chance. Notably, the Vkappa2 family was negatively selected into the productive repertoire. In contrast, the Vkappa1 family was positively selected because of positive selection of three specific genes, O12/O2, L12a and L9. B3 (Vkappa4) and B2 (Vkappa5) were over-represented in the non-productive repertoire and then were expressed less frequently in the productive repertoire. In contrast, the Vkappa3 family gene, A27, was also over-represented in the non-productive repertoire but not further selected into the productive repertoire. Compared to the adult repertoire, junctional diversity was less marked because of a diminished influence of TdT activity, whereas the mean CDR3 length was comparable to that of normal adult B cells. Comparison of the distribution of Vkappa and Jkappa genes with those found in normal adult subjects suggested that there was less receptor editing in neonatal B cells. When neonatal CD5(+) B cells were compared with CD5(-) IgD(+) B cells, it was noted that the Vkappa gene A30 was used only in CD5(+) B cells in both the productive and non-productive repertoires. The results indicate that the usage of Vkappa genes by neonatal B cells is biased by both intrinsic molecular processes and selection. The evidence of selection indicates that the Vkappa repertoire is shaped by self antigens, since exposure to exogenous antigens is limited at the time of birth.

IgM expressed by leukemic CD5(+) B cells binds mouse immunoglobulin light chain

Mouse immunoglobulin (Ig) molecules have previously been shown to bind to the surface of CD5(+) B cells from patients with B-cell chronic lymphocytic leukemia (B-CLL). The results indicated that surface IgM was involved in the interaction and suggested the phenomenon was an example of the polyreactive binding capacity of the surface Ig (sIg) expressed by these malignant cells. This article describes the further characterization of the interaction between human IgM and mouse Ig molecules and subunits. Mouse Ig molecules of both kappa and lambda light chain classes bound to the B-CLL cell surface. The dissociation constant for the interaction of mouse IgG1 (K121) with the B-CLL cell surface was 3.6 x 10(-7) M. To confirm the involvement of the human IgM expressed by the B-CLL cells in the interaction, the malignant cells were stimulated in vitro to induce secretion of human IgM. Enzyme immunoassay was used to show that secreted human IgM bound to intact mouse Ig, as occurred with the cell surface analysis. The mouse Ig epitope recognized by the purified secreted human IgM was shown by Western blot analysis to be located on the light chain of the mouse Ig molecule and to be conformationally dependent. K121 light chain was cloned and expressed in E. coli and the recombinant light chain bound to the surface of CLL B cells. The results confirm that human IgM is the reactive ligand in the interaction with mouse Ig and indicate that the interaction of polyreactive IgM with mouse IgG occurs via the light chain component of IgG.

CD5 expression in human B-cell populations

The origin of CD5+ B cells remains controversial. The differential response to ligation of CD5 resulting in apoptosis or proliferation provides insight into its roles in distinct human B cells. Here, Pierre Youinou, Christophe Jamin and Peter Lydyard review current knowledge of B-1 and B-2 cells, and propose that CD5 has different functions when expressed by different B-cell subpopulations.

CD5 B cells and B-cell malignancies

Over the past year, progress has been made in understanding of the physiology and disease associations of CD5+ (B1) B cells, although their exact role in pathogenesis remains unclear. Earlier studies on the negative function of CD5 within the B-cell receptor complex have been substantiated, and it seems likely that soon the signaling pathways used by this coreceptor will be elucidated. Progress in diagnosis, physiology, and etiopathogenesis of CD5+ malignancies has been made, particularly in B-cell chronic lymphocytic leukemia. The low-level expression of surface immunoglobulin has been explained by the mutations that occur in the associated CD79b. Two new potential tumor-suppressor genes have been identified in the hot spot of chromosome 13q, which provides an exciting step forward in understanding of the etiopathogenesis of some B-cell chronic lymphocytic leukemia. Activated signal transducers for activation of transcription factors molecules have been shown to be phosphorylated on different amino acids in B1 and chronic lymphocytic leukemia tumors, although the significance of this is, as yet, unclear. Finally, aberrant expression of CD40L by chronic lymphocytic leukemia T cells may contribute to the immunodeficiency that develops in these patients.

Age-related changes in blood lymphocyte subsets of Chinese children

BACKGROUND

Flow cytometric analysis of major lymphocyte populations and their subsets reveals age-related changes in the human cellular immune system.

SUBJECTS AND METHODS

Immunophenotypic markers were evaluated in 136 healthy pediatric subjects divided into groups of newborn infants (cord blood), children aged 1 to 2 years, 2 to 5 years, and 6 to 15 years.

RESULTS

The percentage of T cells increased gradually with age and the evolution of the percentage of B and NK cells was found to be variable. The percentage of CD4+ cells remains relatively unchanged from infancy to adolescence, but the percentage of CD8+ T cells was lowest at birth and reached maximal levels in the one to two year-old period. The percentage of naive T cells declined with time, but the percentage of memory T cells increased with age. Similar trends were seen in T-cell receptor alphabeta- and gammadelta-bearing T cells. The percentage of CD 11b+CD8+ T cells increased gradually from birth and reached maximal levels from 6 to 15 years old. The expression of the activation markers CD25 and HLA-DR on CD4+ T cells increased with age. The percentage of CD16+CD56- NK cells declined with age, but the evolution of the percentage of CD 16-CD56+ NK cells was variable. The fraction of B cells that expressed CD5 was high at birth (72.9%) and was highest in one to two year olds (73.1%), then declined steadily over time. The CD23 antigen was expressed on 41.9% of B cells at birth and 68.6% during the first to second year, then declined steadily with age.

CONCLUSION

These data may serve as a reference range for studies of Chinese pediatric subjects.

Pooled Normal Human Polyspecific IgM Contains Neutralizing Anti-Idiotypes to IgG Autoantibodies of Autoimmune Patients and Protects From Experimental Autoimmune Disease

Normal human serum contains IgM antibodies that regulate the natural autoantibody activity of IgG in autologous serum. In the present study, we show that pooled normal human IgM (IVIgM) purified from plasma of more than 2,500 healthy donors and processed in a similar fashion to that of therapeutic preparations of pooled normal human IgG (IVIg) suppresses activity of IgG autoantibodies purified from the serum of patients with autoimmune diseases in vitro. The inhibitory effect of IVIgM was greater or equivalent to that of IVIg on a molar basis. We show that IVIgM contains anti-idiotypic antibodies directed against idiotypic determinants of autoantibodies, in particular by showing that Sepharose-bound IVIgM selectively retained F(ab′)2 fragments of IgG autoantibodies. The infusion of (Lewis × Brown-Norway) F1 rats with IVIgM protected the animals against experimental autoimmune uveitis induced by immunization with the soluble retinal S antigen, as evidenced by clinical scoring and histopathological analysis. The present findings provide a rationale for considering pooled IgM for immunomodulation of autoimmune disease.

Inhibition of the progression of multiple sclerosis by linomide is associated with upregulation of CD4+/CD45RA+ cells and downregulation of CD4+/CD45RO+ cells

In a recent double-blind, phase II study, conducted in our department, we showed that Linomide-treated MS patients had significantly less active lesions (in serial monthly MRI tests) and a tendency for clinical stabilization. Here we present the immunological evaluation of the patients who participated in this study and propose a novel mechanism by which Linomide downregulates autoreactivity. Peripheral blood leukocytes (PBLs), serum, and CSF samples were obtained at two to four time points over the 6 months of the trial. Flow cytometric analysis (FACS) of the CD5/CD19, CD4/CD8, CD14/CD3, CD16/CD3, CD45RA/CD4, and CD45RO/CD4 surface markers on PBLs was performed and the levels of the IL-1beta, IL-2, IL-4, IL-6, IL-10, TNF-alpha, IFN-gamma, and IL-2R were also examined. White blood counts of Linomide-treated patients were consistently elevated throughout the treatment period (P = 0.002-0.04). Cytokines levels in serum and CSF were highly fluctuating and we could not detect any clear trend as a result of Linomide treatment. FACS analysis showed that Linomide treatment significantly increased the percentage of the CD4+/CD45RA+ cells (from 35.5% at baseline to 42.3% at week 24; P = 0.02), and decreased CD4+/CD45RO+ lymphocytes (62.6% at baseline vs 53.7% at week 24, P = 0.02). Linomide also induced a transient increase in the NK-cells, the NK 1.1 cells, and the CD5 B-cells (P = 0.02). Upregulation of naive CD45RA T-lymphocytes and parallel downregulation of memory CD45RO cells seems to be one of the main mechanisms by which Linomide inhibits MS activity and may represent an alternative immunomodulating approach for the treatment of MS and autoimmunity in general.

CD5+ and CD5- B1-like lymphocytes in healthy guinea pig

Spleen, lymph node, and peripheral blood lymphocytes from healthy guinea pigs (gp) were examined for their ability to produce polyreactive autoantibodies to a battery of self-antigens and to cryptic determinants (phosphatidylcholine) on bromelain-treated mouse red blood cells (Br-MRBC). The mouse monoclonal antibody (Mab) 8BE6 anti-gp pan-T (CD5) marker was used for identification of CD5+ B1 cells by the plaque-forming assay (PFC), immunofluorescence, complement-mediated cytotoxicity, and immunocytochemistry. The detection of CD5+ cells by the 8BE6 Mab depended on the method used. They were better demonstrated by cytolysis and immunocytochemistry than by FACS analysis. By the latter method, the level of the CD5+ B cell subpopulation was associated neither with the age of the gp nor with the organ examined. Similarly wide ranges of PFC were detected in untreated or LPS-treated animals regardless of age and organ. The vast majority of the LPS-stimulated IgM antibody-secreting B lymphocytes reacting with the Br-MRBC, and those producing natural autoantibodies, did not bind the 8BE6 Mab.

Polyreactive antigen-binding B cells in the peripheral circulation are IgD+ and B7-

Polyreactive antibodies are naturally occurring antibodies, primarily of the IgM isotype, that are capable of reacting with a wide variety of different self and non-self antigens. Previously, we reported that a B cell capable of making polyreactive antibody has Ig receptors on its surface that can bind different antigens. The present investigation was initiated to characterize these polyreactive antigen-binding B cells further. A panel of fluorescein isothiocyanate-labeled antigens (insulin, IgG Fc fragment or beta-galactosidase) served as probes to select polyreactive antigen-binding B cells by cell sorting. Our experiment revealed that these polyreactive antigen-binding B cells were mainly of the IgD isotype. They expressed high levels of CD40 and major histocompatibility complex class II molecules, but little or no B7-1, B7-2, or Fas. In contrast to the binding of antigens to monoreactive receptors (usually high affinity), the binding of antigens to polyreactive receptors (usually moderate or low affinity) did not up-regulate the expression of B7-1 or B7-2. Antigens that bound to polyreactive receptors, however, were internalized and degraded, although not as efficiently as antigens that bound to monoreactive receptors. Despite the ability of these B7- cells to process antigens, they were not able to activate T cells in a mixed leukocyte reaction. It is concluded that polyreactive antigen-binding B cells have properties that are consistent with the ability to induce immunological tolerance.

Clinical heterogeneity reflects biologic diversity in chronic lymphocytic leukemia

As the incidence of B cell chronic lymphocytic leukemia increases in an aging population, it becomes more important to re-evaluate our understanding of the disease process and current therapy. Previous treatment strategies have been, for the most part, unsuccessful in prolonging survival and thus new approaches are needed. More intense cellular and molecular research on the biologic diversity of this neoplasm will further our understanding of the causes of clinical heterogeneity and refine our ability to predict progression. New approaches, based on alterations of neoplastic cell growth by cytokines or chemotherapeutic agents, may enable clinicians to 'customize' individual treatments based on the stages of CLL B cell differentiation and our understanding of factors involved in the regulation of apoptosis and proliferation at those stages. Taken together, these efforts should ultimately yield much new information that will lead to reduced morbidity and mortality in B-CLL, the most common form of human leukemia.

IgM class autoantibodies in human cord serum

It has previously been shown that human neonatal B lymphocytes in vitro can synthesize autoantibodies which typically are of IgM class, polyreactive and of low affinity and thought to represent natural autoantibodies. We screened 1034 cord serum specimens to find sera with elevated IgM levels; 98 such sera were further examined by an enzyme-linked immunosorbent assay (ELISA) to determine whether antibodies against a panel of autoantigens could be found. We detected low levels of IgM class antibodies against cardiolipin, pyruvate dehydrogenase, single-stranded DNA, thyroglobulin and Fc fragments of IgG as rheumatoid factors. The IgM concentration correlated with autoantibody levels. The specificity of the autoantibody assays was confirmed by inhibition tests. We conclude that several types of autoantibodies can be found in some sera of newborns and that increased IgM concentration of some neonates may reflect a polyclonal antibody response.

Antigen-binding B cells and polyreactive antibodies

The present experiments were initiated to see if cells capable of binding antigens could make polyreactive antibodies. Fluorescein isothiocyanate-labeled self and non-self antigens were incubated with B cells from normal individuals. Antigen-binding cells were separated from non-antigen-binding cells by flow cytometry, immortalized with Epstein-Barr virus and analyzed at the clonal level for their capacity to make polyreactive antibodies. Four to six times more cells making polyreactive antibodies were found in the B cell subset that bound antigens than in the B cell subset that did not bind antigens. The majority of the polyreactive antibodies were of the immunoglobulin (Ig)M isotype. Immunoflow cytometry revealed that cell lines making polyreactive antibodies bound a variety of antigens (e.g., insulin, IgGFc and beta-galactosidase), whereas cell lines making monoreactive antibodies bound only a single antigen. The binding of antigens to B cell lines that made polyreactive antibodies could be inhibited (range, 28%-57%) by both homogeneous and heterogeneous antigens. Both CD5+ and CD5- antigen-binding B cells made polyreactive antibodies, but the frequency was slightly higher in the CD5+ antigen-binding (85%) as compared to the CD5- antigen-binding (50%) population. Comparison of CD5+ B cells that bound antigens with CD5+ B cells that did not bind antigens showed that approximately 86% of the former, but only 15% of the latter, made polyreactive antibodies. It is concluded that cells capable of binding a variety of different antigens can make polyreactive antibodies and that antigen binding is a good marker for identifying polyreactive antibody-producing cells.

The cross-reactive idiotopes recognized by the monoclonal antibodies 9G4 and LC1 are located in framework region 1 of two non-overlapping subsets of human VH4 family encoded antibodies

The monoclonal anti-idiotopic antibodies LC1 and 9G4 bind two non-overlapping sets of VH4 encoded antibodies. 9G4 exclusively binds VH4-21 encoded antibodies, while LC1 binds antibodies derived from VH4 family gene segments V71-2, V71-4, VH4-18, VH72-1 and V2-1. The VH4-21 gene segment is utilized by most cold agglutinin (CA) antibodies with I/i specificity, while antibodies encoded by other VH4 gene segments are associated not with CA disease, but primarily with rheumatoid-factor (RF) activity. We previously determined that the idiotope to which 9G4 binds in VH4-21-derived antibodies is located in framework region 1 (FR1). In the present study, by using mutational analysis involving individual framework- and complementarity-determining region exchanges between VH4-21- and V71-2-encoded antibodies, we have found that the idiotope to which LC1 binds in V71-2-derived antibodies also maps to FR1. The LC1 idiotope is heavy (H)-chain associated, but requires pairing with a light (L) chain for LC1 binding. Recombinant antibodies composed of a variety of kappa (kappa) and lambda (lambda) L chains paired with either a V71-2 or VH4-21 chain were produced in the baculovirus expression system. LC1 bound all of the kappa-containing antibodies but did not bind the V71-2-encoded H chain alone nor to the two lambda-containing antibodies. This experiment demonstrates that not all light chains exert equivalent influence on the conformation of the H-chain idiotope. These results indicate that the FR1 of VH4-encoded antibodies is immunogenic and suggest a physiological role of FR1 during an immune response.

CD5+ B cells and the immune system

The CD5+ B-cell population is prominent in early life and may play a key role in the ontogeny of the immune system. Transplantation studies in mice are in support of CD5+ B cells as a separate lineage from CD5- B cells. In both mice and men there is evidence in favour of CD5 being an activation antigen rather than a lineage marker, but the jury is still out! The frequency of CD5+ B cells appears to be under genetic influence. CD5+ B cells are receptive to many cytokines including IL-2 and IL-5 and themselves produce a number of cytokines especially IL-10. The function of the CD5 molecule on B cells is presently unknown but it might be involved in interaction with CD72 on other B cells. CD5+ B cells generally utilise minimally mutated germ-line genes and produce low avidity auto- and polyreactive antibodies (natural antibodies) generally of the IgM class.

The genetic basis of human VH4 gene family-associated cross-reactive idiotype expression in CD5+ and CD5- cord blood B-lymphocyte clones

In a recent study we have observed a high frequency expression of cross-reactive idiotypes encoded by genes from the relatively small VH4 family of immunoglobulin heavy chain genes in cord blood B-lymphocyte lines. Furthermore, we have demonstrated a selective pattern of expression of two VH4-associated cross-reactive idiotype (CRI) in B-lymphocyte lines established from CD5+ and CD5- cord blood B-lymphocytes. There was a restricted expression of one CRI marker recognized by the 9G4 monoclonal antibody in lines established from CD5+ B-lymphocytes but not in those established from the CD5- population. In the current study we examine the molecular basis for the selective pattern of CRI expression. Nucleotide-sequence analysis of functional immunoglobulin heavy chain (IgH) gene rearrangements in three CD5+ lines expressing the CRI recognised by 9G4 reveal that all use a single gene from the VH4 family, the V4.21 gene. However, all three lines have distinct third complementarity determining regions (CDR3) implying different clonal origins. In contrast, four cord blood cell lines (two established from CD5+ B-lymphocytes) expressing the CRI recognized by MoAb Lc1 have functional IgH gene rearrangements involving two different genes from the VH4 family, the V71-4, and V2-1 genes. Antigen specificity analysis reveals that all three 9G4-reactive lines produce antibodies that react with the I and/or i red blood cell carbohydrate antigens. These data suggest that the distinction in VH4 gene use in CD5+ B-lymphocytes in cord blood results from a selection process in vivo that shapes the repertoire of CD5+ B-lymphocytes. This study extends recent observations that the monoclonal anti-CRI antibodies 9G4 and Lc1 are markers of two distinct subgroups of proteins encoded by two subsets of genes within the VH4 family. Furthermore, it appears that amino acid residues in framework region one and complementarity determining region two are critical for the expression of the cross reactive idiotypes and the serological distinction between the two subgroups of proteins.

Antibodies to the CD5 molecule in normal human immunoglobulins for therapeutic use (intravenous immunoglobulins, IVIg)

IVIg are increasingly used for the treatment of autoimmune diseases. In the present study, we show that IVIg contain antibodies directed against CD5, a cell surface molecule of T cells which is also a marker of the autoantibody-producing CD20+ ('B-1') subset of B lymphocytes. Antibodies to the CD5 molecule were demonstrated in IVIg by the ability of therapeutic preparations of IVIg to inhibit the binding of labelled CD5 MoAb to the CD5-expressing human T cell line H9. Preincubation of H9 cells with IVIg or with F(ab')2 fragments prepared from IVIg resulted in dose-dependent inhibition of the binding of CD5 antibody. The presence in IVIg of antibodies to the CD5 molecule was further confirmed by the binding of IVIg to mouse L cells that expressed human CD5 molecules following a stable transfection with CD5 cDNA. Human CD5 antibodies in IVIg provide therapeutic immunoglobulin preparations with the potential of modulating T cell functions through CD5, and of regulating the expression of B cell subsets expressing CD5. This may have implications for the treatment of autoimmune diseases.

Human CD5-positive B cells in lymphoid malignancy and connective tissue diseases

The current literature on human CD5-positive B cells (CD5 + B cells) has been analysed, with a special emphasis on non organ-specific auto-immune diseases. Malignant cells of most of the chronic lymphoid leukaemias of the B cell lineage express the CD5 molecule. Antibodies of the IgM class produced by leukaemic B cells are multispecific auto-antibodies. The CD5 + B cell subset may be expanded in non organ-specific autoimmune diseases, such as rheumatoid arthritis, primary Sjögren's syndrome, systemic lupus erythematosus. This holds true for various conditions, including organ-specific auto-immune diseases. Since auto-immune features are common in lymphoproliferative disorders, and the latter be a complication in non organ-specific auto-immune diseases, CD5 + B cells may represent an intermediary between these auto-immune diseases and B cell lymphoproliferations. Studies on the regulation of CD5 + B cell production and function are likely to shed light on the aetiology of, and pathogenetic mechanisms operating in the different disease states.

Characterization of lymphocyte subpopulations in cord blood

Twenty-seven cord blood samples from healthy newborns were processed according to a "whole blood" flow cytometric analysis. The CD3-positive T cells were a variable subpopulation representing 44.8 +/- 13.3% of lymphocytes. The majority of the CD3+ cells are CD38+. Newborn T cells have lower levels of both IL-2 receptors and HLA-DR than do adult T cells. The CD4-positive T cells represented 31.0 +/- 10.8% of lymphocytes with a great prevalence of the CD4+/CD45RA+ population. The CD3+/CD8+/CD11b+ cells are increased to 23.4 +/- 7.1% of lymphocytes. The CD57 antigen is not expressed. The NK population, CD16+/CD56+, is increased to 25 +/- 11% of lymphocytes. Of CD19+ cord blood B lymphocytes 68% coexpressed CD5. Thus "suppressive" and "naive" cells are prominently represented in cord blood.

Autoimmunity-prone B-1 (CD5 B) cells, natural antibodies and self recognition

The delineation of distinct subsets committed to the production of antibodies with different antigen-binding activities supports the view of a compartmentalization and specialization of function in the B cell repertoire and is consistent with the hypothesis of a developmentally layered immune system; as originally proposed by Herzenberg and Herzenberg. On the basis of the data by Solvason and Kearney in the human fetus and our data in the adult, and in agreement with the findings of Herzenberg et al. and Hardy et al. in the mouse, we propose that the human B cell repertoire includes at least three distinct B cell subsets: B-1a cells, which develop from progenitors in the fetal splanchnic district, namely the omentum, and are maintained in adult life by virtue of their self-replenishing nature; B-1b cells, progenitors of which can be found in the splanchnic district and, perhaps, adult bone marrow; and, finally, B-2 cells, which arise in the fetal liver and are continuously replenished in adult life by progenitors in the bone marrow (Figure 5). The different B cells types are distinguished by their differential expression of surface CD5 and, perhaps, CD11b and CD14, their differential expression of CD5 mRNA, and the different classes and specificities of the Ig they produce (Figure 5). B-1 lymphocytes play a major role in autoimmunity and constitute the physiological equivalent of the neoplastic forms in various lymphoproliferative disorders, such as CLL and SLL, which are often associated with the production of monoclonal antibodies to self antigens. Human B-1a (CD5+ B) and B-1b (CD5- CD45RAlo B) cells are responsible for the production of natural (polyreactive and monoreactive) antibodies in the fetus, neonate, and adult, and can give rise to the autoantibody-producing cells characteristic of several autoimmune disease states. Our recent findings suggest that while in healthy subjects the majority of natural polyreactive antibodies is encoded in V genes in germline configuration, some polyreactive antibodies are encoded in somatically mutated V genes, in a fashion consistent with an antigen-driven process of selection of such mutations. The nature of the antigen(s) involved in these selection processes remains to be determined. Under possibly different circumstances, the application of an antigen-driven process of clonal selection to B-1a and/or B-1b cells, previously committed to natural antibody production, can result in the generation of monoreactive high affinity and possibly pathogenic autoantibodies (Figures 5A and 5B).(ABSTRACT TRUNCATED AT 400 WORDS)

Prevalence of anti-Fab antibodies in patients with autoimmune and infectious diseases

Sensitive ELISA were devised to examine the specificity of circulating IgM and IgA autoantibodies for whole human IgG, Fc and Fab fragments of human IgG. Sera from patients with autoimmune and infectious conditions such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), tuberculosis (TB), infectious mononucleosis (IM) and cystic fibrosis (CF) were studied. Results of the ELISA assays using whole human IgG as antigen revealed that a proportion of patients in each of the groups studied had circulating IgM and IgA rheumatoid factors (RF). Fifteen normal individuals studied were negative. In the latex positive RA group, IgM RF and IgA RF had primarily anti-Fc reactivity (100% and 93% respectively), although 3/15 patients also showed IgM anti-Fab reactivity and one patient had high IgA anti-Fab activity. Patients with SLE and TB who had detectable RF levels also revealed predominantly anti-Fc specificity. In contrast, examination of 25 patients with IM showed positivity for IgM RF activity in 8% of patients using whole IgG as antigen, 24% positivity using purified Fc fragments as antigen and 45% positivity when plates were coated with Fab fragments. Similarly, a large number of CF patients (54%) also showed predominantly IgM anti-Fab activity. Of interest, 69% of the CF patients who were all studied at the time of bacterial infection had detectable IgA RF levels, with 46% of these patients showing both IgA anti-Fc and anti-Fab activity. These findings suggest that autoantibody specificities in autoimmune and infectious diseases are different.

Repertoire of CD5+ and CD5- cord blood B cells: specificity and expression of VH I and VH III associated idiotopes

Epstein-Barr (EBV)-immortalized B cell clones were established from CD5+ and CD5- cord blood B cells separated by flow cytometry. We have previously shown that IgM from many of the clones was polyreactive, exhibiting reactivity with a number of autoantigens. In this study, IgM produced by the clones was analysed by MoAb for the expression of cross-reactive idiotypes (CRI) associated with rheumatoid factor paraproteins and from defined VH and V kappa subgroups of immunoglobulin heavy and light chains. IgM produced by clones established from CD5+ and CD5- B cells expressed the VH I associated idiotope G8. Furthermore, IgM produced by both sets of clones exhibited a similar frequency of VH III heavy chain subgroup expression, as determined by reactivity with staphylococcal protein A (SpA) and VH III-associated CRI expression (B6 and/or D12). In contrast, expression of the V kappa III-associated 17.109 CRI was significantly higher in IgM antibodies produced by clones established from CD5+ compared with the CD5- clones (32 versus 5%: P less than 0.05). Analysis of the VH and VL subgroup expression by IgM produced by the CD5+ and CD5- cord blood clones, and their autoantigen reactivity profile did not reveal restriction or selection within CD5+ and CD5- populations. However, our data suggest that differences may exist in the expression of certain germ-line genes between CD5+ and CD5- cord blood B cells and might indicate an expansion of CD5+ B cells within the fetal environment.

Specificity and idiotope expression of IgM produced by CD5+ and CD5- cord blood B-cell clones

Epstein-Barr virus (EBV)-immortalized monoclonal B-cell lines were established from CD5+ and CD5- cord-blood B cells. IgM from many of both CD5+ and CD5- clones reacted with IgG-Fc, ssDNA, and a variety of other autoantigens. More CD5+ B cells that used light chains of the kappa isotype reacted with IgG-Fc and ssDNA than kappa-bearing CD5- B cells. Because many of the clones reacted with IgG-Fc, they were analyzed for the expression of cross-reactive idiotypes (CRI) associated with rheumatoid factor and cold agglutinin paraproteins using murine antibodies (mAb) recognizing V kappa and VH subgroup-associated determinants. Expression of the V kappa IIIb sub-subgroup-associated idiotope recognized by 17.109 mAb was expressed at significantly higher frequency (32%; p less than 0.05) and IgM antibodies derived from the CD5+ compared with the CD5- clones (5%). Both CD5+ and CD5- clones expressed the RF paraprotein-associated idiotope recognized by G8 mAb to the same extent. Similar results were obtained using binding to SpA as a marker of VH III family usage. Furthermore, no differences in frequency of expression of RF paraprotein-associated idiotopes recognized by B6 and/or D12, and characteristic of some antibodies using VH III family genes, were found between the CD5+ and CD5- populations. Although a higher than expected frequency of VH IV-gene expression was demonstrated (around 30%) in both CD5+ and CD5- cells, there were differences in expression of CRI recognized by mAb Lc1 and R2.1A2 with specificities for two VH IV subfamilies. While some CD5+ and CD5- clones were identified in which their IgM reacted with mAb Lc1, only CD5+ clones were recognized by another mAb R2.1A2. Analysis of the relationships between antigen specificities and V kappa- and VH-family gene usage indicated that auto- or polyreactivity was not associated with V kappa III nor any particular VH family. The higher frequency of the V kappa IIIb sub-subgroup-associated idiotope recognized by 17-109 in the CD5+ clones and the association of CD5+ B cells with the VH IV subfamily recognized by mAb R2.1A2 and 9G4 may suggest that CD5+ B cells in cord blood are expanded as a result of recruitment within the fetal environment.

Age-related changes in human blood lymphocyte subpopulations

Flow cytometric analysis of major lymphocyte populations and their subsets reveals age-related changes in the cellular human immune system. Immunophenotypic markers were evaluated in 110 normal pediatric subjects, divided into groups of newborn infants, infants aged 2 days to 11 months, and children aged 1 to 6 years and 7 to 17 years; results were then compared with those obtained from 101 normal adults aged 18 to 70 years. Comparisons among age groups from newborn infants through adults reveal progressive declines in the absolute numbers of leukocytes, total lymphocytes, and T, B, and natural killer (NK) cells. The percentages of T cells within the total lymphocyte population increase with age, in both CD4+ and CD8+ subsets. Percentages of B and NK cells are higher in newborn infants than in adults. The expression of the activation markers interleukin-2R and HLA-DR on T cells increases with age, as does the NK-associated expression of CD57 on CD8 cells. The proportions of B lymphocytes that coexpress CD5 or CDw78 decrease with age, whereas expression of Leu-8 and CD23 increases. The proportion of CD4 cells bearing the CD45RA and Leu-8 markers is consistently lower in adults than in children. These data may serve as a reference range for studies of pediatric subjects.

Cell-free CD5 in patients with rheumatic diseases

Since an increased frequency of CD5+ B cells has been reported in rheumatoid arthritis (RA) and primary Sjögren's syndrome (SS), and the expression of the molecule was reduced on the T cells of some SS patients, we hypothesised that there would be an accelerated turnover of CD5 in these disorders. We describe a novel enzyme-linked immunosorbent assay for measuring cell-free (CF) CD5, using rabbit F(ab')2 anti-CD5 antibody as capture agent and monoclonal anti-CD5 antibody as revealing agent. It was established that CF-CD5 was detectable in RA and SS sera, as opposed to sera from patients with ankylosing spondylitis and normal controls. The level of CF-CD5 did not correlate with rheumatoid factor in RA patients but was significantly higher (P less than 0.05) in SS patients with extraglandular manifestations than in those with glandular disease. Three of the latter patients with significantly increased levels of CD5-negative T cells did not have a particularly high proportion of CF-CD5 in these sera.