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Secretory immunoglobulins and their transport
Published in Phillip D. Smith, Richard S. Blumberg, Thomas T. MacDonald, Principles of Mucosal Immunology, 2020
Charlotte S. Kaetzel, Jiri Mestecky, Jenny M. Woof
Another bacterial strategy to evade the mucosal IgA response employs surface proteins, termed IgA-binding proteins, that bind specifically to both serum and secretory forms of human IgA. Such proteins are expressed by strains of group A streptococcus (Streptococcus pyogenes), an important pathogen causing acute infections sometimes resulting in compromised heart and kidney function; group B streptococcus, a major cause of septicemia, meningitis, and pneumonia in newborn babies; and Staphylococcus aureus, responsible for skin infections, abscesses, pneumonia, bacteremia, and other illnesses, many of which are life-threatening. Remarkably, although the IgA-binding proteins produced by these organisms are structurally unrelated, they all interact with broadly the same region of IgA Fc. Their sites of interaction on the Fc region of IgA overlap with that bound by FcαRI, and their binding has been shown to block binding of IgA to this receptor and inhibit triggering of FcαRI-mediated responses. This inhibitory capability suggests that these bacteria have evolved IgA-binding protein expression as a means to evade elimination mechanisms elicited by IgA through interaction with FcαRI.
Eosinophil Membrane Receptors: Function of IgE- and IgA-Binding Molecules
Published in Gerald J. Gleich, A. Barry Kay, Eosinophils in Allergy and Inflammation, 2019
Monique Capron, Marie-José Truong, Pierre Desreumaux, Bouchaïb Lamkhioued, Margherita Tomassini, André Capron
In addition to the classic FcaR, which binds to serum IgA, a saturable binding site for purified secretory component has been detected on eosinophils. Granule proteins can be released after exposure of eosinophils to antihuman IgE and antihuman IgA antibodies or to the specific antigen. However, no correlation was observed between EPO and ECP release, suggesting a differential release of these two mediators according to the stimulus of activation. Various experimental procedures indicate that the preferential mediator release induced by secretory IgA is due to the binding of secretory component and the subsequent activation of eosinophils. Taken together, these findings point to the effector function of eosinophils in local and mucosal immunity.
Innate and adaptive barrier properties of airway mucus
Published in Anthony J. Hickey, Heidi M. Mansour, Inhalation Aerosols, 2019
Alison Schaefer, Samuel K. Lai
sIgA has four binding sites, giving it greater crosslinking capacity. Both secretory component and the higher presence of IgA2 contribute to a greater resistance of the antibody against bacterial degradation (75–77). sIgA contributes to antigen neutralization at all three levels of the mucosal tissues: the lumen, the epithelium, and the lamina propria. In the lumen, sIgA can agglutinate bacteria into aggregates that are too large to penetrate through the pores of mucus to inhibit adherence of bacteria at the epithelial surface, a process frequently referred to as immune exclusion. sIgA can also directly neutralize viruses both in the mucus layer and intraepithelially. dIgA can also bind antigen in the lamina propia, and the immune complex is then cleared to the lumen via binding with pIgR and subsequent endocytosis (Figure 15.7) (78–81). FcαRI, an IgA Fc receptor present on myeloid immune cells, can bind to IgA-opsonized pathogens, resulting in a proinflammatory immune response.
Analysis of Inflammatory and Homeostatic Roles of Tissue-resident Macrophages in the Progression of Cholesteatoma by RNA-Seq
Published in Immunological Investigations, 2021
Lian Fang, Lin Chen, Bi Lin, Liang Han, Kaiquan Zhu, Qifa Song
Regarding the inflammatory and anti-infection roles of TRMØs, the current findings, through condensing data from up-regulated genes, GO processes, to biological networks, as well as KEGG pathways, mainly consisted of activated neutrophil function, activated B cell, T cell immunity, and extracellular matrix organization. Several KEGG pathways were proved to be up-regulated, including lysosome, pathogenic Escherichia coli infection, Staphylococcus aureus infection, TNF signaling pathway, cytokine-cytokine receptor interaction, B cell receptor signaling pathway, etc. These up-regulated KEGG pathways suggested that chronic bacterial infections and down-stream signaling cascades contributed to this illness. These pathogens were largely opportunistic bacteria on the skin. Especially, the top-rank expression of the Fc fragment of IgA receptor (FCAR) was a strong signal for increased mucosal immunity.
Reformatting palivizumab and motavizumab from IgG to human IgA impairs their efficacy against RSV infection in vitro and in vivo
Published in mAbs, 2018
Shamir R. Jacobino, Maaike Nederend, J. Frederiek Reijneveld, Daan Augustijn, J. H. Marco Jansen, Jan Meeldijk, Karli R. Reiding, Manfred Wuhrer, Frank E. J. Coenjaerts, C. Erik Hack, Louis J. Bont, Jeanette H. W. Leusen
Since FcRs may also be involved in antibody-mediated elimination of virus-infected cells in vivo, as previously shown by Ravetch and colleagues for FcγRs and IgG targeting influenza HA,7 we aimed to investigate the involvement of FcαRI in IgA in vivo protection against RSV infection. However, as mice lack a homologue of human FcαRI,24 we used human FcαRI transgenic mice, which express this receptor on their myeloid cells.25 Palivizumab IgA prophylaxis in FcαRI transgenic mice did not result in better protection against RSV infection compared to wild-type mice (Fig. 5A). Consequently, the recombinant motavizumab antibodies were tested only in wild-type mice. As observed with palivizumab, motavizumab IgG seemed to be slightly more effective than the motavizumab IgA antibodies, but none of the differences in RSV load between motavizumab IgG and IgA treatment were statistically significant (Fig. 5B).
CD89-mediated recruitment of macrophages via a bispecific antibody enhances anti-tumor efficacy
Published in OncoImmunology, 2018
Bingyu Li, Lijun Xu, Chenyu Pi, Yanxin Yin, Kun Xie, Fei Tao, Renhao Li, Hua Gu, Jianmin Fang
FcαRI (CD89) is constitutively expressed on monocytes/macrophages, eosinophils, and neutrophils; however, importantly, it is not expressed on non-effector cell populations.8 The known functions of FcαRI include ADCC, phagocytosis, induction of respiratory bursts, and inflammatory mediator or cytokine release.9 Notably, FcαRI has been proven to be more efficient in triggering tumor cell killing than FcγRI. The capacity of FcαRI and FcγRI to initiate polymorphonuclear (PMN) cell signaling has been investigated. Cross-linking of FcαRI resulted in a more rapid induction of an increase in intracellular free calcium levels than cross-linking of FcγRI.10