Role of Protein Kinase A Activation in the Immune System with an Emphasis on Lipopolysaccharide-Responsive and Beige-like Anchor Protein in B Cells.

Cyclic AMP-dependent protein kinase A (PKA) is a ubiquitous enzymatic complex that is involved in a broad spectrum of intracellular receptor signaling. The activity of PKA depends on A-kinase anchoring proteins (AKAPs) that attach to PKAs close to their substrates to control signaling. Although the relevance of PKA-AKAP signaling in the immune system is evident in T cells, its relevance in B and other immune cells remains relatively unclear. In the last decade, lipopolysaccharide-responsive and beige-like anchor protein (LRBA) has emerged as an AKAP that is ubiquitously expressed in B and T cells, specifically after activation. A deficiency of LRBA leads to immune dysregulation and immunodeficiency. The cellular mechanisms regulated by LRBA have not yet been investigated. Therefore, this review summarizes the functions of PKA in immunity and provides the most recent information regarding LRBA deficiency to deepen our understanding of immune regulation and immunological diseases.

Lrba participates in the differentiation of IgA+ B lymphocytes through TGFßR signaling.

Introduction: Lrba is a cytoplasmic protein involved in vesicular trafficking. Lrba-deficient (Lrba-/-) mice exhibit substantially higher levels of IgA in both serum and feces than wild-type (WT) mice. Transforming growth factor ß1 (TGFß1) and its receptors (TGFßR I and II) is essential for differentiating IgA+ B cells. Furthermore, increased IgA production suggests a potential connection between Lrba and the TGFßR signaling pathway in IgA production. However, the specific function of Lrba in B cell biology remains unknown. Aim: Given the increased IgA levels in Lrba-/- mice, the goal in this work was to explore the lymph organs where the switch to IgA occurs, and if TGFßR function is affected. Methods: Non-immunized Lrba-/- mice were compared with Lrba+/+ mice. IgA levels in the serum and feces, as well as during peripheral B cell development, were determined. IgA+ B cells and plasma cells were assessed in the small intestine and secondary lymphoid organs, such as the spleen, mesenteric lymph nodes, and Peyer's patches. The TGFßR signaling pathway was evaluated by determining the expression of TGFßR on B cells. Additionally, SMAD2 phosphorylation was measured under basal conditions and in response to recombinant TGFß. Finally, confocal microscopy was performed to investigate a possible interaction between Lrba and TGFßR in B cells. Results: Lrba-/- mice exhibited significantly higher levels of circulating IgA, IgA+ B, and plasma cells than in peripheral lymphoid organs those in WT mice. TGFßR expression on the membrane of B cells was similar in both Lrba-/- and Lrba+/+ mice. However, intracellular TGFßR expression was reduced in Lrba-/- mice. SMAD2 phosphorylation showed increased levels under basal conditions; stimulation with recombinant TGFß elicited a poorer response than in that in Lrba+/+ B cells. Finally, we found that Lrba colocalizes with TGFßR in B cells. Conclusion: Lrba is essential in controlling TGFßR signaling, subsequently regulating SMAD2 phosphorylation on B cells. This mechanism may explain the increased differentiation of IgA+ B cells and production of IgA-producing plasma cells.

Improved HUMARA for the Detection of X-Linked Agammaglobulinemia Carriers.

Background: Fragment analysis of exon 1 of the human androgen receptor, known as HUMARA, is a polymerase chain reaction (PCR)-based method for detecting X-linked agammaglobulinemia (XLA) carriers. This method takes advantage of X-chromosome inactivation (XCI) in female cells. XLA is caused by mutations in the Bruton tyrosine kinase (BTK) gene, located in Xq22.1. In this study, XCI is nonrandom or skewed in B-cells. B-cells with an active X-chromosome carrying a BTK mutation do not mature. Peripheral B-cells in XLA carriers inactivate the mutated X-chromosome. Methods: HUMARA was performed using DNA from purified B-cells and total leukocytes. DNA was digested using methylation-sensitive HhaI. The PCR of the HUMARA polymorphic marker was performed with the HhaI digested samples. The lengths of the PCR products were determined. If a suspected carrier showed skewed XCI in their B-cells, the marker length that corresponded with the length determined in the index patient indicated their carrier status. Results: HUMARA was conducted on purified B-cells; this allowed easier identification of the mutated or inactive allele, as the active allele was enzymatically digested. Analysis of 30 possible carriers using modified HUMARA corroborated that the carrier status in all samples that were heterozygous for the marker using XCI calculation for leukocytes showed a Gaussian distribution, while the carrier B-cell DNA showed a skewed XCI. Conclusion: Carrier status was successfully determined for most of the analyzed samples. B-cell enrichment resulted in precise carrier determination data, reduced the sample size, and facilitated inactive and active allele identification.