Characterization of the ligand binding site of the bovine IgA Fc receptor (bFc alpha R)

The immunomodulatory effect of lactulose on Enterococcus faecium fed preruminant calves

Prebiotics and probiotics could represent an effective alternative to the use of synthetic antibiotics in nutrition. The mechanisms by which prebiotics affect the immune system have not yet been investigated in detail. Most effects have been attributed to increases in the innate and acquired immune responses. This study was conducted to elucidate the long-term effects of orally administered lactulose on the immune response in the intestinal tract of probiotic-fed calves. Preruminant calves were randomized to 3 feeding groups: milk replacer containing 1) no lactulose, 2) 1% lactulose, or 3) 3% lactulose. All 3 milk replacers contained 10(9) cfu Enterococcus faecium/kg. Messenger RNA expression of different cell activation markers, pro- and antiinflammatory cytokines, and IgA Fc receptor was investigated in the ileum, mesenterial lymph node, spleen, and white blood cells. A significantly greater number of blood lymphocytes were detected in the 3% lactulose group (P = 0.02) than in the control group. The expression results in male calves indicated that the transcription of IgA Fc receptor in the ileal mucosa of the 1% lactulose treatment group increased significantly (P = 0.04) and also tended to increase in the 3% lactulose group (P = 0.07). Furthermore, decreases in IL-10 and interferon-gamma mRNA expression were observed in the ileum (P = 0.04). The CD4-presenting lymphocytes were decreased significantly in the ileum (P = 0.04) and mesenteric lymph node (P = 0.01), whereas CD8-presenting lymphocytes were increased in the blood (P = 0.03) of females. Other proinflammatory cytokines (IL-1beta, IL-8, and tumor necrosis factor-alpha) and antiinflammatory cytokines (transforming growth factor-beta1) did not show significant differences in mRNA expression among treatment groups. The results indicate that additional lactulose feeding had an immunomodulatory effect on the composition of T-cell subsets in different immune compartments and had minor effects on pro- and antiinflammatory cytokine mRNA expression.

Unknown functions of immunoglobulins A

Traditionally, the function of immunoglobulins A (IgA), the major type of secreted antibodies, has been thought to be restricted to binding antigens outside the epithelium basal membrane. Therefore, effector mechanisms eliminating IgA-opsonized targets have not been investigated so far. However, some indirect observations of infectious agents penetrating into tissues and blood from the environment suggest such mechanisms (analogous to IgG/IgM-dependent activation of complement and natural killers). In the present review, we examine details of IgA structure that might contribute to elucidation of IgA-dependent effector functions in human and animal immunity. Special attention is given to a putative transduction of signal about antigen binding in the active center of IgA from the Fab- to the Fc-superdomain via intramolecular conformational rearrangements. Different structure of the IgA subclasses (IgA1 and IgA2) is examined taking into account probable divergence of their functions in immune response.

Identification of the linear epitope for Fc-binding on the bovine IgG2 Fc receptor (boFcgamma2R) using synthetic peptides

To identify the linear epitope for Fc-binding on the bovine IgG2 Fc receptor (boFcgamma2R), peptides derived from the membrane-distal extracellular domain (EC1) of boFcgamma2R corresponding to the homologous region of human FcalphaRI were synthesized. Binding of bovine IgG2 to the different peptides was tested by Dot-blot assay, and the peptide showing maximal binding was further modified by truncation and mutation. The minimum effective peptide 82FIGV85 located in the putative F-G loop of the EC1 domain was found to bind bovine IgG2 specifically and inhibit the binding of bovine IgG2 to the receptor. The Phe82, Ile83 and Val85 residues within the linear epitope were shown to be critical for IgG2-binding. Such functional epitope peptide should be very useful for understanding the IgG-Fcgamma interaction and development of FcR-targeting drugs.

IgA Fc receptors in cattle and horses

The biological role of IgA depends, at least partly, on the interaction with specific receptors (FcalphaRs) on the surface of leukocytes. The human FcalphaR, CD89, was the first IgA Fc receptor to be identified, and binding of IgA-coated particles to CD89 triggers numerous cellular effector functions including phagocytosis, antibody-dependent cell-mediated cytotoxicity (ADCC), and release of inflammatory mediators. Recently, CD89 orthologs have been identified in a number of other species, including cows and horses. This brief review will summarize our current knowledge regarding the structure and function of bovine and equine CD89.

Cloning and characterization of equine CD89 and identification of the CD89 gene in chimpanzees and rhesus macaques

Immunoglobulin A (IgA) is the major antibody class present in external secretions of mammals. At the vulnerable mucosal surfaces, IgA provides a crucial first-line defence by neutralizing pathogens. Primates also have a substantial level of IgA in serum and although not well understood, the biological role of this IgA depends, at least partly, on its ability to interact with specific receptors (FcalphaRs) on the surface of leucocytes. The human FcalphaR, CD89, was the first IgA Fc receptor to be identified and binding of IgA-coated particles to CD89 triggers numerous cellular effector functions, including phagocytosis, antibody-dependent cellular cytotoxicity, and release of inflammatory mediators, all of which may play an important role in both systemic and mucosal immunity. For many years humans were the only species known to express CD89, however, it has recently been cloned from cows and rats. Here, we describe the identification of the CD89 gene in three additional species: horses, chimpanzees, and Rhesus macaques. Equine CD89 was identified at the cDNA level, whereas the chimpanzee and Rhesus macaque genes were identified from the available draft genomic sequence. Interestingly, when compared with humans and other primates, horses, cows and rats have a relatively low concentration of serum IgA, so the role of CD89 in these species is of particular interest. The identification and characterization of CD89 in different species will contribute to a greater understanding of the biological role of IgA and CD89 in mucosal and systemic immunity throughout evolution.