Isotypes and specificities of immunoglobulins produced by germ‐free mice fed chemically defined ultrafiltered “antigen‐free” diet

Abstract

The regulation of the "spontaneously" occurring ("background") Ig synthesis of mice has been studied by determining the numbers of IgM-, IgG- and IgA-secreting cells and a part of the IgM antibody-specificity repertoire in spleen, bone marrow (BM) and mesenteric lymph nodes (MLN) of conventional and "antigen-free" mice. These antigen-free mice were germ-free raised and fed an ultrafiltered solution of chemically defined low molecular weight nutrients, and thus devoid of exogenous antigenic stimulation. The secretion of IgM, IgG and IgA by spleen, BM and MLN cells was assessed in the protein A plaque assay, while specific IgM antibody-secreting cells were detected by plaque assays specific for differently haptenated sheep red blood cells. In general, antigen-free and conventional mice were found to have roughly equal numbers of IgM-secreting cells in spleen and BM. The number of IgG-secreting cells in the spleen of antigen-free mice was the same as in the spleen of conventional mice, but in the BM their number was 3-5-fold decreased. About one half of the antigen-free mice did not have MLN, and in the half which did, 5 times less IgM- and more than 100-fold less IgG-secreting cells were found as compared with conventional mice. The number of IgA-secreting cells in antigen-free mice was drastically decreased in all three organs tested. The antibody-specificity repertoire of the "background" IgM-secreting cells in the spleen and BM of the antigen-free and conventional mice was much alike. This indicates that in antigen-free mice the available antibody repertoires are established independently of exogenous and/or mitogenic stimulation.

Diversification of Ig Heavy Chain Genes in Human Preterm Neonates Prematurely Exposed to Environmental Antigens

“…In mice living in a sterile environment and consuming an ultrafiltered low Ag diet (germfree Agfree mice), IgM levels were nearly normal and the IgM repertoire showed a normal diversity. But levels of circulating IgG and IgA were profoundly depressed and peripheral lymph nodes and mucosal lymphoid tissue were smaller than in conventionally housed animals (31,32).…”

TLR Agonists Selectively Promote Terminal Plasma Cell Differentiation of B Cell Subsets Specialized in Thymus-Independent Responses

“…For example, a recent report from Pasare and Medzhitov (25) has demonstrated that MyD88-deficient mice express normal serum IgA Abs (although IgA secretion in the gut had not been explored). Furthermore, contradictory results have been published regarding the reduction of serum IgM levels in naive MyD88-deficient mice or MyD88/TRIF doubledeficient mice (25,26), and natural Abs are still produced in germfree mice (27,28). It cannot formerly be excluded that formation and replenishment of the pool of natural Abs involves compensatory mechanisms other than TLR signaling or that TLRs can be triggered by endogenous ligands.…”

Expression of Natural Autoantibodies in MRL-lpr Mice Protects from Lupus Nephritis and Improves Survival

“…However, it remains a paradox that Abs reactive with self-constituents are found in abundance in normal sera. Such Abs are thought to arise naturally without exogenous Ag stimulation, as they are present in cord blood and in newborn humans and mice, as well as in mice housed in germ-free conditions and fed an Ag-free diet (15)(16)(17)(18). They are therefore referred to as natural autoantibodies (NAA).…”