Elevated cerebrospinal fluid IgA in humans and rats is not associated with secretory component

Increased plasma and brain immunoglobulin A in Alzheimer’s disease is lost in apolipoprotein E ε4 carriers

Background

Alzheimer’s disease (AD) is foremost characterized by β-amyloid (Aβ)-extracellular plaques, tau-intraneuronal fibrillary tangles (NFT), and neuroinflammation, but over the last years it has become evident that peripheral inflammation might also contribute to the disease. AD patients often demonstrate increased levels of circulating proinflammatory mediators and altered antibody levels in the blood. In our study, we investigated the plasma Immunoglobulin A (IgA) levels in association with apolipoprotein E (APOE) ε4 status and Aβ pathology.

Methods

IgA levels in antemortem-collected (cohort I) and postmortem-collected (cohort II) plasma samples from AD patients (n = 30 in cohort I and n = 16 in cohort II) and non-demented age-matched controls (NC) (n = 42 in cohort I and n = 7 in cohort II) were measured using ELISA. Hippocampal sections from cohort II were immunostained against IgA, and the IgA area fraction as well as the number of IgA positive (IgA+) cells in the cornu ammonis region were analysed using ImageJ. The relationship between plasma IgA levels and cognition, C-reactive protein (CRP), and cerebrospinal fluid (CSF) AD biomarkers in cohort I as well as neuropathology, IgA+ cell number, and IgA area fraction in cohort II was analysed before and after grouping the cohorts into APOEε4 carriers and APOEε4 non-carriers.

Results

Plasma IgA levels were higher in AD patients compared to NC in both cohorts. Also, AD patients demonstrated higher IgA area fraction and IgA+ cell number compared to NC. When APOEε4 status was considered, higher plasma IgA levels in AD patients were only seen in APOEε4 non-carriers. Finally, plasma IgA levels, exclusively in APOEε4 non-carriers, were associated with cognition, CRP, and CSF Aβ levels in cohort I as well as with IgA area fraction, IgA+ cell number, and Aβ, Lewy body, and NFT neuropathology in cohort II.

Conclusions

Our study suggests that AD pathology and cognitive decline are associated with increased plasma IgA levels in an APOE allele-dependent manner, where the associations are lost in APOEε4 carriers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01062-z.

Evaluation of a microsphere-based immunofluorescence assay for the determination of Immunoglobulin A concentrations in cerebrospinal fluid of dogs

The simultaneous increase of immunoglobulin A (IgA) in serum and cerebrospinal fluid (CSF) is a characteristic finding in dogs suffering from canine steroid-responsive meningitis-arteritis (SRMA). The study aimed at developing and evaluating a microsphere-based immunofluorescence assay (MIA) for the measurement of IgA, trying to fulfill the need of a quicker method using only small volumes of CSF. Microsphere beads were coated with goat-anti-dog IgA antibodies and bound IgA was detected by a mouse-anti-dog IgA antibody in combination with a PE-labeled goat-anti-mouse IgG. CSF from 44 dogs were tested for IgA and compared with an in-house utilized ELISA. Using clinical relevant reference ranges, the new method showed a good agreement (84.17%) with the ELISA. A method comparison revealed a moderate agreement only. These findings indicate that the MIA will not replace the ELISA, but it opens the possibility for further research with microsphere-based assays.

Antigen-Dependent Intrathecal Antibody Synthesis in the Normal Rat Brain: Tissue Entry and Local Retention of Antigen-Specific B Cells

The intrathecal Ab response to Ag introduced into the normal brain has not been fully explored. Involvement of Ag-specific, peripheral B cells in an intrathecal response was studied using a normal rat model of Ag infusion through an indwelling cannula into defined brain sites, while maintaining a functionally intact blood-brain barrier. Specific Ab was detected in serum and cerebrospinal fluid. The intrathecal response is first detectable at day 14. Isoelectric focusing of cerebrospinal fluid reveals banding patterns consistent with local Ab production. To increase Ag-specific, circulating peripheral lymphocytes available for trafficking to Ag-stimulated brain and for enhancing intrathecal Ab synthesis, rats were preimmunized peripherally. Subsequently, Ag or saline (control) was infused through the cannula. Under this protocol, intrathecal synthesis is detectable earlier (day 5 postinfusion). Immunohistochemical studies at the infusion site assessed Ag-specific B cells, T cells, and activated APCs. Rats receiving peripheral preimmunization followed by Ag into caudate nucleus have far greater numbers of these cells, including plasma cells, within the infusion site compared with saline controls. Results confirm previous indirect evidence of intrathecal Ab synthesis in normal rat brain and provide the first direct evidence for B cell trafficking across normal brain barriers plus retention at the Ag deposition site. Our studies indicate that the normal brain microenvironment supports development of Ag-directed humoral immunity. We propose that immune privilege in normal brain is characterized by down-regulation of cell-mediated but not Ab immune responses within the central nervous system.

Neuroimmunology of tics and other childhood hyperkinesias

The etiology of tics and other childhood hyperkinesias is unclear despite attempts to link these movement disorders to neurotransmitter abnormalities and genes. This article will review the studies that suggest that some movement disorders are the result of immunologic factors.

Fluoxetine treatment alters leukocyte trafficking in the intrathecal compartment of the young primate

To evaluate possible long-term effects of exposure to monoaminergic drugs, blood and cerebrospinal fluid (CSF) samples were collected from adolescent monkeys that had been treated with desipramine and fluoxetine in infancy. This evaluation focused on the number and type of leukocytes in CSF as a reflection of cell trafficking in the intrathecal compartment. Monkeys administered fluoxetine 2 years prior to the sample collection evinced significantly higher numbers of leukocytes in CSF than did either control or desipramine-treated subjects. The elevated cell count was accounted for primarily by increased numbers of CD4+ and CD8+ lymphocytes. The finding of higher cell numbers in CSF was replicated in a second sample from the fluoxetine-treated monkey obtained 1.5 years later. Because the cell profile in blood was unaffected by the prior drug treatments, these observations indicate a need for further study of serotonergic influences on regulation of the intrathecal compartment in the developing individual.

Determination of total and herpes simplex virus specific monomeric and dimeric IgA in serum and cerebrospinal fluid by ultracentrifugation

An improved method is described for differentiating between monomeric and dimeric total and herpes simplex virus (HSV) specific IgA by ultracentrifugation in sucrose gradient, using recovery and quantitative analysis of the fractions obtained. Calculation of monomeric and dimeric IgA was based on IgG as an internal standard. Intrathecally produced monomeric and dimeric IgA were judged by calculating IgA indices for each form. A new type of formula indicating relative over-production of dimeric compared with monomeric IgG (IgA dimeric-monomeric index) is suggested. The method was applied to serum and cerebrospinal fluid (CSF) from three patients with HSV encephalitis. The index for monomeric as well as dimeric IgA was high during the acute phase of the disease, indicating intrathecal synthesis of both molecular forms. One year after onset, there was no detectable HSV-specific IgA in CSF: both molecular forms, however, remained in serum. The amount of dimeric compared with monomeric IgA was high during the acute phase, and subsequently decreased after successful treatment. A new finding was the detection of HSV-specific IgA heavier than dimeric IgA in serum one year after onset of the disease. These components may be tetrameric IgA, or immune complexes containing IgA.

Intrathecal production of specific IgA antibodies in CNS infections

Cerebrospinal fluid (CSF) and serum from subjects with herpes simplex encephalitis, herpes zoster, mumps meningitis and neuroborreliosis were analysed for the presence of immunoglobulin A (IgA) and G (IgG) antibodies to the corresponding four antigens. Specific intrathecal IgA antibody synthesis as manifested by an elevated index was a frequent finding. Higher IgA index values than the corresponding IgG was seen in one third of the samples from subjects with herpes simplex encephalitis and herpes zoster. Correlation between specific IgG and IgA index was most pronounced for varicella-zoster virus (r = 0.66, P < 0.001). In subjects with mumps meningitis a strong intrathecal IgA and IgG antibody response to Borrelia burgdorferi was demonstrated. Specific herpes simplex and varicella-zoster virus IgA was not found to contain secretory component, thus contradicting an active secretion into the CNS compartment. In conclusion, our data indicate that specific IgA is intrathecally produced in herpes simplex encephalitis, herpes zoster and mumps meningitis but is a rare finding in neuroborreliosis.