Viral load determines the B-cell response in the cerebrospinal fluid during human immunodeficiency virus infection

Main lymphocyte subpopulations in cerebrospinal fluid and peripheral blood in HIV-1 subtypes C and B

HIV-1 subtype C (HIV-1C) shows reduced Tat protein chemoattractant activity compared with HIV-1B. The impact of HIV-1C Tat on the chemotaxis of the main lymphocyte subpopulations in the cerebrospinal fluid (CSF) and the peripheral blood (PB) is unclear. We hypothesized that there would be a lower frequency of specific lymphocyte subpopulations CD3⁺ or CD19⁺ in CSF in HIV-1C than in HIV-1B. The objectives were to detect the differences in the proportions of main lymphocyte subpopulations in CSF and PB, between people with HIV (PWH) and HIV-1-uninfected volunteers (PWoH) and in HIV-1B and HIV-1C. Lymphocyte immunophenotyping was studied in CSF and paired PB samples of PWH (n = 22) and PWoH (n = 14). Lymphocytes were analyzed within the CD45⁺ gated region. The proportions of CSF CD3⁺CD4⁺, CD3⁺CD8⁺, and CD3^-CD19⁺ lymphocytes in CSF were comparable in HIV-1B and C. There was an increase in the proportion of CD3⁺CD8⁺ cells and a decrease in CD3⁺CD4⁺ T cells (ps = 0.016) in the CSF samples of the PWH compared with the PWoH group. In the PWH group, both CD3⁺CD4⁺ and CD3⁺CD8⁺ lymphocytes were significantly higher in the CSF than in the PB (p = 0.047 and 0.005). The proportion of CD3⁺CD4⁺ was lower and that of CD3⁺CD8⁺ was higher in the CSF samples of the aviremic group than that of HIV-negative control (p = 0.0008 and < 0.0001, respectively). HIV-1C Tat substitution (C30S) did not interfere with the CNS migration of the main lymphocyte subpopulations. This is the first study to evaluate these lymphocytes in CSF and PB of HIV-1C compared with HIV-1B.

Viremia controls Env-specific antibody-secreting cell responses in simian immunodeficiency virus infected macaques pre and post-antiretroviral therapy

OBJECTIVE

The aim of this study was to investigate the kinetics of Env (gp140)-specific antibody-secreting cells (ASCs) during acute and early chronic simian immunodeficiency virus (SIV) infection, and prior to and postantiretroviral therapy (ART) in rhesus macaques.

DESIGN AND METHODS

At week 0, rhesus macaques were inoculated intravenously with SIVmac239 and the viral loads were allowed to develop. Daily ART was initiated at week 5 post infection until week 18, though the animals were monitored until week 28 for the following parameters: enumeration of SIV gp140-specific ASCs by ELISPOT; quantification of viremia and SIV gp140-specific IgG titres through qRT-PCR and ELISA, respectively; estimation of monocytes, follicular helper T cells (Tfh) and memory B cell frequencies using polychromatic flow cytometry.

RESULTS

Direct correlations were consistently found between blood SIV gp140-specific ASC responses and viremia or SIV Env-specific IgG titres. In contrast, SIV gp140-specific ASC responses showed inverse correlations with the percentage of total memory B cells in the blood. In lymph nodes, the magnitude of the SIV gp140-specific ASC responses also followed the viral load kinetics. In contrast, the number of SIV gp140-specific ASCs presented did not correlate with frequencies of circulating activated monocyte (CD14+CD16+) or Tfh cells.

CONCLUSION

Blood and/or lymph node viral loads may regulate the onset and magnitude of SIV gp140-specific ASCs during SIV infection and following ART in rhesus macaques.

IgG intrathecal synthesis in HIV-associated neurocognitive disorder (HAND) according to the HIV-1 subtypes and pattern of HIV RNA in CNS and plasma compartments

We hypothesized that humoral immunity stimulation in the CNS in HIV-1C patients would be lower than that in HIV-1B due to a defective Tat chemokine dimotif (C30C31) that might influence cellular trafficking and CNS inflammation. Sixty-eight paired CSF and blood samples from people with HIV (PWH), free of CNS opportunistic infections, were included, HIV-1B (n = 27), HIV-1C (n = 26), and HIV negative (n = 25). IgG intrathecal synthesis was assayed using quantitative and qualitative methods. IgG oligoclonal bands (OCB) in CSF were observed in 51% of PWH, comparable between HIV-1B and HIV-1C, as well as the medians of IgG intrathecal synthesis formulas. The group with HIV infection aviremic in CSF and blood showed 75% of OCB. There was a poor positive correlation between the IgG quotient and GDS. The impact of HIV-1 on IgG intrathecal production was not subtype dependent. Low-grade CNS intrathecal IgG production persists in HIV CNS infection even in PWH with CSF and blood HIV RNA controlled.

Recent Advances in Neuromyelitis Optica Spectrum Disorder: Pathogenesis, Mechanisms and Potential Treatments

Neuromyelitis optica spectrum disorder (NMOSD) is an acute or subacute demyelinating disease that affects mainly the optic nerve and spinal cord. A major proportion of NMOSD cases have a relationship with autoimmunity to aquaporin 4 (AQP4) found on the central nervous system. NMOSD can occur repeatedly, causing symptoms such as decreased vision and weakness of limbs. The main goal of current therapy is to relieve acute symptoms and prevent recurrence of the disease. Without timely and appropriate treatment, the recurrence and disability rates are high. In the present work, we review recent advances in the diagnosis and treatment of patients with NMOSD, as well as the pathogenesis and mechanisms of AQP4-IgG-seropositive NMOSD.

B Cell Compartmentalization in Blood and Cerebrospinal Fluid of HIV-Infected Ugandans with Cryptococcal Meningitis

Activated B cells modulate infection by differentiating into pathogen-specific antibody-producing effector plasmablasts/plasma cells, memory cells, and immune regulatory B cells. In this context, the B cell phenotypes that infiltrate the central nervous system during human immunodeficiency virus (HIV) and cryptococcal meningitis coinfection are ill defined. We characterized clinical parameters, mortality, and B cell phenotypes in blood and cerebrospinal fluid (CSF) by flow cytometry in HIV-infected adults with cryptococcal (n = 31) and noncryptococcal (n = 12) meningitis and in heathy control subjects with neither infection (n = 10). Activation of circulating B cells (CD21low) was significantly higher in the blood of subjects with HIV infection than in that of healthy controls and greater yet in matched CSF B cells (P < 0.001). Among B cell subsets, elevated frequencies of memory and plasmablasts/plasma cells most clearly distinguished the CSF from blood compartments. With cryptococcal meningitis, lower frequencies of expression of the regulatory protein programmed death-1 (PD-1) on plasmablasts/plasma cells in blood (median, 7%) at presentation were associated with significantly decreased 28-day survival (29% [4/14 subjects]), whereas higher PD-1 expression (median, 46%) characterized subjects with higher survival (88% [14/16 subjects]). With HIV infection, B cell differentiation and regulatory markers are discrete elements of the circulating and CSF compartments with clinical implications for cryptococcal disease outcome, potentially due to their effects on the fungus and other local immune cells.

Flavivirus-Mediating B Cell Differentiation Into Antibody-Secreting Cells in Humans Is Associated With the Activation of the Tryptophan Metabolism

Patients infected with the Dengue virus (DENV) often present with a massive generation of DENV-specific antibody-secreting cells (ASCs) in the blood. In some cases, these ASCs represent more than 50% of the circulating B cells, a higher magnitude than those induced by other infections, vaccinations, and plasma cell lymphomas. However, it remains unclear how the DENV infection elicits this colossal response. To address this issue, we utilised an in vitro strategy to induce human PBMCs of healthy individuals incubated with DENV particles (DENV4 TVP/360) to differentiate into ASCs. As controls, PBMCs were incubated with a mitogen cocktail or supernatants of uninfected C6/36 cells (mock). The ASC phenotype and function were increasingly detected in the DENV and mitogen-cultured PBMCs as compared to mock-treated cells. In contrast to the in vivo condition, secreted IgG derived from the PBMC-DENV culture was not DENV-specific. Lower ASC numbers were observed when inactivated viral particles or purified B cells were added to the cultures. The physical contact was essential between B cells and the remaining PBMCs for the DENV-mediated ASC response. Considering the evidence for the activation of the tryptophan metabolism detected in the serum of Dengue patients, we assessed its relevance in the DENV-mediated ASC differentiation. For this, tryptophan and its respective metabolites were quantified in the supernatants of cell cultures through mass spectrophotometry. Tryptophan depletion and kynurenine accumulation were found in the supernatants of PBMC-DENV cultures, which presented enhanced detection of indoleamine 2,3-dioxygenase 1 and 2 transcripts as compared to controls. In PBMC-DENV cultures, tryptophan and kynurenine levels strongly correlated to the respective ASC numbers, while the kynurenine levels were directly proportional to the secreted IgG titers. Contrastingly, PBMCs incubated with Zika or attenuated Yellow Fever viruses showed no correlation between their kynurenine concentrations and ASC numbers. Therefore, our data revealed the existence of distinct pathways for the DENV-mediated ASC differentiation and suggest the involvement of the tryptophan metabolism in this cellular process triggered by flavivirus infections.

To B or Not to B: Understanding B Cell Responses in the Development of Malaria Infection

Malaria is a widespread disease caused mainly by the Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) protozoan parasites. Depending on the parasite responsible for the infection, high morbidity and mortality can be triggered. To escape the host immune responses, Plasmodium parasites disturb the functionality of B cell subsets among other cell types. However, some antibodies elicited during a malaria infection have the potential to block pathogen invasion and dissemination into the host. Thus, the question remains, why is protection not developed and maintained after the primary parasite exposure? In this review, we discuss different aspects of B cell responses against Plasmodium antigens during malaria infection. Since most studies have focused on the quantification of serum antibody titers, those B cell responses have not been fully characterized. However, to secrete antibodies, a complex cellular response is set up, including not only the activation and differentiation of B cells into antibody-secreting cells, but also the participation of other cell subsets in the germinal center reactions. Therefore, a better understanding of how B cell subsets are stimulated during malaria infection will provide essential insights toward the design of potent interventions.

Compartmentalized intrathecal immunoglobulin synthesis during HIV infection - a model of chronic CNS inflammation?

HIV infects the central nervous system (CNS) during primary infection and persists in resident macrophages. CNS infection initiates a strong local immune response that fails to control the virus but is responsible for by-stander lesions involved in neurocognitive disorders. Although highly active anti-retroviral therapy now offers an almost complete control of CNS viral proliferation, low-grade CNS inflammation persists. This review focuses on HIV-induced intrathecal immunoglobulin (Ig) synthesis. Intrathecal Ig synthesis early occurs in more than three-quarters of patients in response to viral infection of the CNS and persists throughout the course of the disease. Viral antigens are targeted but this specific response accounts for <5% of the whole intrathecal synthesis. Although the nature and mechanisms leading to non-specific synthesis are unknown, this prominent proportion is comparable to that observed in various CNS viral infections. Cerebrospinal fluid-floating antibody-secreting cells account for a minority of the whole synthesis, which mainly takes place in perivascular inflammatory infiltrates of the CNS parenchyma. B-cell traffic and lineage across the blood-brain-barrier have not yet been described. We review common technical pitfalls and update the pending questions in the field. Moreover, since HIV infection is associated with an intrathecal chronic oligoclonal (and mostly non-specific) Ig synthesis and associates with low-grade axonal lesions, this could be an interesting model of the chronic intrathecal synthesis occurring during multiple sclerosis.

Has CXCL13 an added value in diagnosis of neurosyphilis?

In patients with syphilis, central nervous system (CNS) involvement is often difficult to determine. In patients who also are infected with human immunodeficiency virus (HIV), this is even more challenging, as cerebrospinal fluid (CSF) pleocytosis can be attributed to HIV, syphilis, or both. Hence, this study investigated (i) CSF chemokine (C-X-C motif) ligand 13 (CXCL13) as a potential marker to diagnose neurosyphilis in HIV-infected individuals and (ii) the added value of CSF CXCL13 to conventional CSF biomarkers, such as the rapid plasma reagin test (RPR), in diagnosing neurosyphilis. We included 103 syphilis patients from two centers in The Netherlands: 47 non-HIV-infected patients and 56 HIV-infected patients. A positive CSF-RPR was regarded as the gold standard for neurosyphilis. CSF CXCL13 levels were significantly higher in neurosyphilis patients when neurosyphilis was diagnosed by CSF-RPR (P = 0.0002) than in the syphilis control group. The sensitivity and specificity of CSF CXCL13 (cutoff of 76.3 pg/ml) to diagnose neurosyphilis by using positive CSF-RPR as the gold standard were 50% and 90%, respectively. CSF CXCL13 had an added value to CSF-RPR positivity in 70% of HIV-positive patients and in 33% of HIV-negative patients. Our data show that CSF CXCL13 might be a potential additional marker in neurosyphilis when other markers are not conclusive. The added value of CSF CXCL13 measurement to the current neurosyphilis gold standard appears to benefit HIV-positive patients more than HIV-negative patients.

Immune cell subtyping in the cerebrospinal fluid of patients with neurological diseases

The analysis of cerebrospinal fluid (CSF) with the assessment of CSF cell counts and proteins is an important method in the diagnostic workup of neurological diseases. As an addition to this standard approach, we here present data on the distribution of CSF immune cell subsets in common neurological diseases, and provide reference values along with cases of rare neurological diseases. CD4+ and CD8+ T cells, the CD4/CD8 ratio, B cells, plasmablasts, monocytes and NK cells in the CSF of 319 patients with inflammatory or non-inflammatory neurological diseases were analysed by seven-color flow cytometry. Diagnoses included headache, idiopathic intracranial hypertension, Guillain-Barré syndrome, multiple sclerosis, Lyme neuroborreliosis, bacterial and viral meningitis, human immunodeficiency virus (HIV) infection, stroke, and CNS malignancies, among others. T cells were the predominant population in the CSF with CD4+ T cells being more prevalent than CD8+ T cells. Mostly in HIV patients, and under other conditions of immunosuppression, CD4+ and CD8+ T cells were significantly altered and the CD4/CD8 ratio reduced. B cells and plasmablasts could hardly be detected in non-inflammatory diseases but were consistently elevated in inflammatory diseases. Monocytes were reduced in neuroinflammation and showed a negative correlation with B cells. NK cells were slightly elevated in neuroinflammation. Both monocytes and NK cells were slightly elevated in CNS malignancies. The analysis of immune cell subsets in the CSF adds valuable information to clinicians and is a promising tool for the differential diagnosis of neurological diseases.

Cellular Composition of Cerebrospinal Fluid in HIV-1 Infected and Uninfected Subjects

In order to characterize the cellular composition of cerebrospinal fluid (CSF) in a healthy state and in the setting of chronic pleocytosis associated with HIV-1 (HIV) infection, multi-parameter flow cytometry was used to identify and quantitate cellular phenotypes in CSF derived from HIV-uninfected healthy controls and HIV-infected subjects across a spectrum of disease and treatment. CD4+ T cells were the most frequent CSF population and the CD4:CD8 ratio was significantly increased in the CSF compared to blood (p = 0.0232), suggesting preferential trafficking of CD4+ over CD8+ T cells to this compartment. In contrast, in HIV-infection, CD8+ T cells were the major cellular component of the CSF and were markedly increased compared to HIV-uninfected subjects (p<0.001). As with peripheral blood, the CSF CD4:CD8 ratio was reversed in HIV-infected subjects compared to HIV-uninfected subjects. Monocytes, B cells and NK cells were rare in the CSF in both groups, although absolute counts of CSF NK cells and B cells were significantly increased in HIV-infected subjects (p<0.05). Our studies show that T cells are the major cellular component of the CSF in HIV-infected and uninfected subjects. The CSF pleocytosis characteristic of HIV infection involves all lymphocyte subsets we measured, except for CD4+ T cells, but is comprised primarily of CD8+ T cells. The reduced proportion of CD4+ T cells in the CSF may reflect both HIV-related peripheral loss and changes in trafficking patterns in response to HIV infection in the central nervous system.

Identification of peptide targets in neuromyelitis optica

Neuromyelitis optica (NMO) is an inflammatory demyelinating disease that predominantly affects the optic nerves and spinal cord. Recombinant antibodies (rAbs) generated from clonally expanded plasma cells in an NMO patient are specific to AQP4 and pathogenic. We screened phage-displayed peptide libraries with these rAbs, and identified 14 high affinity linear and conformational peptides. The linear peptides shared sequence homologies with NMO autoantigen AQP4 on the extracellular surface. Competitive inhibition ELISA and immunocytochemistry demonstrated that these peptides represent epitopes of NMO autoantigen AQP4. Peptide epitopes/mimotopes may have potential uses for disease prognosis, monitoring, and therapy.

Neurological disease: the effects of HIV and antiretroviral therapy and the implications for early antiretroviral therapy initiation

PURPOSE OF REVIEW

The purpose of this review is to examine the literature regarding HIV-associated neurocognitive disorders, early HIV infection of the central nervous system (CNS), the role of the peripheral immune system in controlling HIV infection and disease within the brain and the potential role that early antiretroviral treatment may play in the preservation of neurocognitive health in patients with more than 500 CD4+ cells/microl.

RECENT FINDINGS

In the post highly active antiretroviral therapy (HAART) era, HIV-associated neurocognitive disorders remain prevalent and even mild-moderate immunosuppression carries a risk for the development of HIV-associated dementia. HIV infection of the CNS occurs early in the illness, and data suggest that a robust peripheral immune system is key to the long-term control of CNS HIV infection. HAART results in clinical, neuropsychological and neuroradiological improvement in patients with HIV-associated neurocognitive disorders, and the prescription of HAART regimens with good cerebrospinal fluid penetration appears to be preferable in this setting. There is little evidence that HAART causes CNS toxicity. The benefits and risks of HAART in the preservation or enhancement of neurocognitive function in well, HIV-infected patients with more than 500 CD4+ cells/microl are unknown.

SUMMARY

The prescription of HAART in well, HIV-infected patients with high CD4+ cell counts may afford enhanced control of CNS HIV infection as a result of the benefits of HAART upon peripheral immune function. In turn, this may result in superior or preserved neurocognitive performance in comparison to the current practice of commencing HAART when CD4+ cells reach 350 cells/microl or lower. This hypothesis will be tested in an upcoming randomized clinical trial.

B cells and antibodies in MS

Increasing research activities on humoral immune responses involved in the immunopathogenesis of multiple sclerosis (MS) led to a revival of the importance of B cells and antibodies in MS. B cells seem now to play various immunopathogenetic roles in the initiation and propagation of inflammatory demyelinating processes at different disease stages of MS. The biological activities of antibodies in MS is, in general, still less known, although it emerges that antibodies are specifically involved in demyelination or, at least, mirror tissue destruction in the central nervous system. Finally, there is growing evidence that treatments, which specifically target B cells and/or antibodies, are effective in MS and its variants neuromyelitis optica (NMO). This chapter therefore aims to summarize the present knowledge and to outline future directions about the role of B cells and antibodies in research and therapy of MS and NMO.

Intrathecal pathogenic anti-aquaporin-4 antibodies in early neuromyelitis optica

OBJECTIVE

The serum of most neuromyelitis optica (NMO) patients contains autoantibodies (NMO-IgGs) directed against the aquaporin-4 (AQP4) water channel located on astrocyte foot processes in the perivessel and subpial areas of the brain. Our objectives were to determine the source of central nervous system (CNS) NMO-IgGs and their role in disease pathogenesis.

METHODS

Fluorescence-activated cell sorting and single-cell reverse transcriptase polymerase chain reaction were used to identify overrepresented plasma cell immunoglobulin (Ig) sequences in the cerebrospinal fluid (CSF) of an NMO patient after a first clinical attack. Monoclonal recombinant antibodies (rAbs) were generated from the paired heavy and light chain sequences and tested for target specificity and Fc effector function. The effect of CSF rAbs on CNS immunopathology was investigated by delivering single rAbs to rats with experimental autoimmune encephalomyelitis (EAE).

RESULTS

Repertoire analysis revealed a dynamic, clonally expanded plasma cell population with features of an antigen-targeted response. Using multiple independent assays, 6 of 11 rAbs generated from CSF plasma cell clones specifically bound to AQP4. AQP4-specific rAbs recognized conformational epitopes and mediated both AQP4-directed antibody-dependent cellular cytotoxicity and complement-mediated lysis. When administered to rats with EAE, an AQP4-specific NMO CSF rAb induced NMO immunopathology: perivascular astrocyte depletion, myelinolysis, and complement and Ig deposition.

INTERPRETATION

Molecular characterization of the CSF plasma cell repertoire in an early NMO patient demonstrates that AQP4-specific Ig is synthesized intrathecally at disease onset and directly contributes to CNS pathology. AQP4 is now the first confirmed antigenic target in human demyelinating disease.

Frequency and phenotype of human immunodeficiency virus envelope-specific B cells from patients with broadly cross-neutralizing antibodies

Induction of broadly cross-reactive neutralizing antibodies (NAb) is an important goal for a prophylactic human immunodeficiency virus type 1 (HIV-1) vaccine. Some HIV-infected patients make a NAb response that reacts with diverse strains of HIV-1, but most candidate vaccines have induced NAb only against a subset of highly sensitive isolates. To better understand the nature of broad NAb responses that arise during natural infection, we screened patients for sera able to neutralize diverse HIV strains and explored the frequency and phenotype of their peripheral Envelope-specific B cells. We screened 113 HIV-infected patients of various clinical statuses for the prevalence of broad NAb. Sera able to neutralize at least four of five viral isolates were found in over one-third of progressors and slow progressors, but much less frequently in aviremic long-term nonprogressors. Most Env-specific antibody-secreting B cells were CD27(hi) CD38(hi) plasmablasts, and the total plasmablast frequency was higher in HIV-infected patients than in uninfected donors. We found that 0.0031% of B cells and 0.047% of plasmablasts secreted Env-specific immunoglobulin G (IgG) in an enzyme-linked immunospot (ELISPOT) assay. We developed a novel staining protocol to label HIV-specific B cells with Env gp140 protein. A total of 0.09% of B cells were found to be Env-specific by this method, a frequency far higher than that indicated by ELISPOT assay. gp140-labeled B cells were predominantly CD27(+) and surface IgG(+). These data describe the breadth and titer of serum NAb and the frequency and phenotype of HIV-specific B cells in a cohort of patients with broad cross-neutralizing antibody responses that are potential goals for vaccines for HIV.

Cerebrospinal fluid B cells correlate with early brain inflammation in multiple sclerosis

BACKGROUND

There is accumulating evidence from immunological, pathological and therapeutic studies that B cells are key components in the pathophysiology of multiple sclerosis (MS).

METHODOLOGY/PRINCIPAL FINDINGS

In this prospective study we have for the first time investigated the differences in the inflammatory response between relapsing and progressive MS by comparing cerebrospinal fluid (CSF) cell profiles from patients at the onset of the disease (clinically isolated syndrome, CIS), relapsing-remitting (RR) and chronic progressive (CP) MS by flow cytometry. As controls we have used patients with other neurological diseases. We have found a statistically significant accumulation of CSF mature B cells (CD19+CD138-) and plasma blasts (CD19+CD138+) in CIS and RRMS. Both B cell populations were, however, not significantly increased in CPMS. Further, this accumulation of B cells correlated with acute brain inflammation measured by magnetic resonance imaging and with inflammatory CSF parameters such as the number of CSF leukocytes, intrathecal immunoglobulin M and G synthesis and intrathecal production of matrix metalloproteinase (MMP)-9 and the B cell chemokine CxCL-13.

CONCLUSIONS

Our data support an important role of CSF B cells in acute brain inflammation in CIS and RRMS.