High-affinity IgM+ memory B cells are defective in differentiation into IgM antibody-secreting cells by re-stimulation with a T cell-dependent antigen

Comprehensive method for producing high-affinity mouse monoclonal antibodies of various isotypes against (4-hydroxy-3-nitrophenyl)acetyl (NP) hapten

Monoclonal antibody (mAb) technology has significantly contributed to basic research and clinical settings for various purposes, including protective and therapeutic drugs. However, a rapid and convenient method to generate high-affinity antigen-specific mAbs has not yet been reported. Here, we developed a rapid, easy, and low-cost protocol for antigen-specific mAb production from single memory B cells. Using this method, high-affinity IgG1 mAbs specific to the hapten 4-hydroxy-3-nitrophenylacetyl (NP) were established from NP-CGG immunized C57BL/6 mice within 6 days. Our mAb production system allows flexible switching of IgG1 to any other isotype with the same paratope, enabling the absolute quantification of antigen-specific serum antibody titers and affinity maturation. Additionally, we established a protocol for the production of IgM and IgA, retaining their functional pentamer and dimer structures. This method is also effective against human antigens and pathogens, making it a powerful tool for mAb development in both research and clinical settings.

B cell subsets were associated with prognosis in elderly patients with community acquired pneumonia

BACKGROUND

The role of B cell subsets remained to be elucidated in a variety of immune diseases, though which was used as an effective biomarker for anti-inflammatory or antiviral response. This study aimed to evaluate the early changes of B cell subtypes distribution in elderly patients with community acquired pneumonia (CAP), as well as the association between B cell subtypes and prognosis.

METHODS

This prospective study included elderly patients with CAP, severe CAP (sCAP) and healthy elderly subjects between April 2016 and March 2018. Flow cytometry was used to detect CD3, CD20, HLA-DR, CD24, CD27, CD38, IgM, and IgD. CD20⁺ B cells were further divided into naïve B cells (Bn), IgM/D⁺ memory B cells (IgM⁺ Bm), switched B cells (SwB), and transitional B cells (Btr).

RESULTS

A total of 22 healthy controls, 87 patients with CAP and 58 patients with sCAP were included in the study. Compared to CAP, sCAP was characterized by significantly lower absolute number of B cells, Bn and Btr, significantly lower Btr and Bn subset percentage, while percentage of IgM⁺ Bm was significantly higher. Heat map showed Bn and Btr on day 3 and day 7 was negatively correlated with activated partial prothrombin time (APTT), international normalized ratio (INR), sequential organ failure assessment score (SOFA) and Acute Physiology and Chronic Health Evaluation II (APACHE II). After 28-day follow-up, Btr percentage in survival group was significantly higher. Receiver operator characteristic (ROC) curve analysis found that Btr count showed sensitivity of 48.6% and specificity of 87.0% for predicting the 28-day survival, with an area under the ROC curves of 0.689 (p = 0.019).

CONCLUSIONS

Severity and prognosis of CAP in elderly people is accompanied by changes in the B cell subsets. Btr subsets could play prognostic role for a short-term mortality of elderly CAP patients.

Immunoglobulin M in Health and Diseases: How Far Have We Come and What Next?

B lymphocytes are important in secreting antibodies that protect against invading pathogens such as viruses, bacteria, parasites, and also in mediating pathogenesis of allergic diseases and autoimmunity. B lymphocytes develop in the bone marrow and contain heavy and light chains, which upon ligation form an immunoglobulin M (IgM) B cell receptor (BCR) expressed on the surface of naïve immature B cells. Naïve B cells expressing either IgM or IgD isotypes are thought to play interchangeable functions in antibody responses to T cell-dependent and T cell-independent antigens. IgM short-lived plasma cells (SLPCs) and antigen-specific IgM memory B cells (MBCs-M) are critical in the first few days of infection, as well as long-term memory induced by vaccination, respectively. At mucosal surfaces, IgM is thought to play a critical part in promoting mucosal tolerance and shaping microbiota together with IgA. In this review, we explore how IgM structure and BCR signaling shapes B cell development, self and non-self-antigen-specific antibody responses, responses to infectious (such as viruses, parasites, and fungal) and non-communicable diseases (such as autoimmunity and allergic asthma). We also explore how metabolism could influence other B cell functions such as mucosal tolerance and class switching. Finally, we discuss some of the outstanding critical research questions in both experimental and clinical settings targeting IgM.