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Antibodies of the immunoglobulin M (IgM) class represent the frontline of humoral immune responses. They are secreted as planar polymers in which flanking µ2L2 "monomeric" subunits are linked by two disulfide bonds, one formed by the penultimate cysteine (C575) in the tailpiece of secretory µ chains (µstp) and the second by C414 in the Cµ3. The latter bond is not present in membrane IgM. Here, we show that C575 forms a non‐native, intra‐subunit disulfide bond as a key step in the biogenesis of secretory IgM. The abundance of this unexpected intermediate correlates with the onset and extent of polymerization. The rearrangement of the C‐terminal tails into a native quaternary structure is guaranteed by the engagement of protein disulfide isomerase ERp44, which attacks the non‐native C575 bonds. The resulting conformational changes promote polymerization and formation of C414 disulfide linkages. This unusual assembly pathway allows secretory polymers to form without the risk of disturbing the role of membrane IgM as part of the B cell antigen receptor. Synopsis: While membrane IgM are inserted into B‐cell receptors as µ2L2 "monomers", only IgM polymers are secreted in primary humoral immune responses. This study uncovers an unexpected step in secretory IgM biogenesis. A highly conserved code of hydrophobic aminoacids, a sugar and cysteine 575 in secretory µ chain tailpieces dictate IgM polymerization.IgM polymerization entails formation of a non‐native disulfide bond linking two cysteines 575 within a secretory µ2L2 subunit.ERp44 attacks the intra‐subunit disulfide and enhances IgM polymerization.The non‐native disulfide bond promotes further inter‐subunit bonding via Cys414. [ABSTRACT FROM AUTHOR]

Abstract Background Recurrent and persistent infections are known to affect airways of patients with Primary Immunodeficiency despite appropriate replacement immunoglobulin serum levels. Interestingly, patients with Chronic Obstructive Pulmonary Disease or with non-CF bronchiectasis also show similar susceptibility to such infections. This may be due to the limited availability of immunoglobulins from the systemic circulation in the conductive airways, resulting in local immunodeficiency. Topical application of nebulized plasma-derived immunoglobulins may represent a means to address this deficiency. In this study, we assessed the feasibility of nebulizing plasma-derived immunoglobulins and delivering them into the airways of rats and non-human primates. Methods Distinct human plasma-derived immunoglobulin isotype preparations were nebulized with an investigational eFlow® nebulizer and analyzed in vitro or deposited into animals. Biochemical and immunohistological analysis of nebulized immunoglobulins were then performed. Lastly, efficacy of topically applied human plasma-derived immunoglobulins was assessed in an acute Streptococcus pneumoniae respiratory infection in mice. Results Characteristics of the resulting aerosols were comparable between preparations, even when using solutions with elevated viscosity. Neither the structural integrity nor the biological function of nebulized immunoglobulins were compromised by the nebulization process. In animal studies, immunoglobulins levels were assessed in plasma, broncho-alveolar lavages (BAL) and on lung sections of rats and non-human primates in samples collected up to 72 h following application. Nebulized immunoglobulins were detectable over 48 h in the BAL samples and up to 72 h on lung sections. Immunoglobulins recovered from BAL fluid up to 24 h after inhalation remained structurally and functionally intact. Importantly, topical application of human plasma-derived immunoglobulin G into the airways of mice offered significant protection against acute pneumococcal pneumonia. Conclusion Taken together our data demonstrate the feasibility of topically applying plasma-derived immunoglobulins into the lungs using a nebulized liquid formulation. Moreover, topically administered human plasma-derived immunoglobulins prevented acute respiratory infection.

The content of the J peptide of secretory polymeric immunoglobulins can significantly change during various pathologies, reflecting the state of the adaptive immune system. In this study, the content of J peptide was determined in various tissues of healthy people. These results can be used as basic data for investigations of the changes in the content of J peptide during different pathologies. [ABSTRACT FROM AUTHOR]

Background: Functional polymorphisms of immunoglobulin G (IgG) Fc receptors (FcγR) have been shown to be associated with generalized aggressive periodontitis (GAgP) or recurrence of chronic periodontitis (CP) in Japanese patients. The purpose of this study was to evaluate whether FcγR polymorphisms are also associated with severity of CP., Methods: Fifty Japanese non-smoking patients with severe CP and 39 Japanese non-smoking patients with moderate CP were identified according to established clinical criteria, including measurements of probing depth (PD), clinical attachment level (CAL), and alveolar bone loss (BL). FcγR genotypes for 3 bi-allelic polymorphisms (FcγRIIa-R/H131, FcγRIIIa-158V/F, FcγRIIIb-NA1/NA2) were determined in these CP patients and 64 race-matched, non-smoking healthy controls by means of allele-specific polymerase chain reactions., Results: There was a significant over-representation of FcγRIIIa-158V allele in severe CP patients compared to moderate CP patients (odds ratio 2.03, 95% confidence interval [CI] 1.03-4.01, χ 2 = 4.86, P = 0.028). In addition, we found a strong association between CP severity and FcγR composite genotype comprising FcγRIIIa-158V plus FcγRIIIb-NA2 (severe CP versus moderate CP: odds ratio 4.69, 95% CI 1.52-15.10, χ 2 = 9.35, P = 0.002; severe CP versus healthy controls: odds ratio 4.10, 95% CI 1.62-10.59, χ 2 = 11.13, P = 0.0009). Moreover, CP patients positive for the composite genotype exhibited more severe signs of periodontitis than composite genotype-negative individuals (positive versus negative; mean PD: 3.8 mm versus 3.2 mm, P = 0.005; mean CAL: 4.5 mm versus 3.7 mm, P = 0.005; mean % BL: 37.6% versus 29.9%, P = 0.008)., Conclusion: Our results document the FcγRIIIa-158V allele and possibly FcγRIIIb-NA2 to be associated with severity of CP in Japanese patients. J Periodontol 2001;72:1324-1331., (© 2001 American Academy of Periodontology.)