The vast diversity of bacteria that inhabit the gastrointestinal tract strongly influence host physiology, not only nutrient metabolism but also immune system development and function. The complexity of the microbiota is matched by the complexity of the host immune system, where they have coevolved to maintain homeostasis ensuring the mutualistic host-microbial relationship. Numerous studies in recent years investigating the gut-brain axis have demonstrated an important role for the gut microbiota in modulating brain development and function, with the immune system serving as an important coordinator of these interactions. Gut bacteria can modulate not only gut-resident immune cells but also brain-resident immune cells. Activation of the immune system in the gut and in the brain are implicated in responses to neuroinflammation, brain injury, as well as changes in neurogenesis and plasticity. Impairments in this bidirectional communication are implicated in the etiopathogenesis of psychiatric and neurodevelopmental diseases and disorders, including autism spectrum disorders, or comorbidities associated with Gastrointestinal diseases, including inflammatory bowel diseases, where dysbiosis is commonly seen. Consequently, probiotics, or beneficial microbes, are being recognized as promising therapeutic targets to modulate behavior and brain development by modulating the gut microbiota. Here we review the role of microbiota-immune interactions in the gut and the brain during homeostasis and disease and their impact on gut-brain communication, brain function, and behavior as well as the use of probiotics in central nervous system alterations.Statement of novelty: The microbiota-gut-brain axis is increasingly recognized as an important physiological pathway for maintaining health and impacting the brain and central nervous system. Increasing evidence suggests that the immune system is crucial for gut-brain signaling. In this review, we highlight the critical studies in the literature that identify the key immune pathways involved.

Background: Patients with chromosome 18 abnormalities can present with an immune phenotype that resembles common variable immunodeficiency. Knowledge of the genes underlying the immune defects related to chromosome 18 aberrations could improve our understanding of the molecular basis of primary antibody deficiencies. Here we present a patient with ring chromosome 18 affected by primary antibody deficiency and autoimmunity.Methods: Lymphocyte populations were determined by flow cytometry. Specific antibody response to protein vaccines and pneumococcal capsule antigen were measured by ELISA. Genome sequencing was performed using a PCR-free protocol.Case: The patient was diagnosed with ring chromosome 18 for delayed growth and dysmorphic features at the age of 1 month. Array comparative genomic hybridization showed deletions of 18p11.21-pter and 18q21.31-qter. At the age of 10 months, she started having recurrent episodes of otitis media and pneumonia, as well as autoimmune arthritis. Serum immunoglobulins and specific antibody levels were low. The CD19+CD27+ memory B cell and CD45RO+ T cell populations were decreased. Recurrent infections were controlled with parenteral immunoglobulin and autoimmune arthritis was treated with systemic and intra-articular therapies.Conclusions: Selective IgA deficiency is the most common form of immunodeficiency associated with chromosome 18 abnormalities, however patients with ring chromosome 18 may also be affected by specific antibody deficiency and require immunoglobulin replacement for optimal care. These patients might partially share the same genomic loss as in patients with non-syndromic primary antibody deficiency.Statement of novelty: This report highlights an important teaching point about immune deficiency in a chromosomal anomaly that is not infrequently encountered in pediatric hospitals. Furthermore, our investigations provide more insight into the pathogenesis of immunodeficiency among patients with chromosome 18 abnormalities.

Background: Artemis enzyme, encoded by the DCLRE1C gene, is essential to V(D)J recombination in both T and B lymphocytes. Artemis functions as an important component of the nonhomologous end-joining DNA double-strand break repair pathway. Artemis deficiency leads to a T-B-NK+ severe combined immune deficiency (SCID) associated with radiosensitivity.Clinical presentation: We present a case of a positive newborn screen for SCID in a patient who was subsequently shown to have a T-B-NK+ phenotype. Further immune evaluation showed profound T and B lymphopenia, near-absent response to mitogen stimulation, and absent immunoglobulins A and M. Genetic investigation demonstrated a novel and putative pathogenic variant in the DCLRE1C gene.Conclusion: This case identifies a novel variant in the DCLRE1C gene in a patient with SCID identified by newborn screening.Statement of novelty: This case report identifies a novel variant in the DCLRE1C gene in a patient with T-B-NK+ SCID.