Lactobacillus casei Cell Wall Extract and Production of Galactose-Deficient IgA1 in a Humanized IGHA1 Mouse Model.

Key Points: We generated a transgenic mouse model expressing the human IgA1 heavy chain, which has a hinge region with rich -linked glycosylation. After inflammatory stimulation, the mouse model showed elevated galactose-deficient IgA1 levels in the serum. Coupled with complement H factor mutant, the mice model exhibited glomerular lesions, associated with hematuria and albuminuria like IgA nephropathy.

Background: IgA nephropathy is the most common primary glomerulonephritis worldwide, and there is emerging evidence linking galactose-deficient IgA1 (Gd-IgA1) to the pathogenesis of the disease. However, mouse models that can be used to study Gd-IgA1's origin of production, biochemical characteristics, and immune reactivity are lacking.

Methods: We generated a humanized IgA1 mouse model with transgenic expression of the human gene from the mouse chromosomal locus of IgA heavy chain. The mice were crossed with complement factor H heterozygous mutant (FH) to generate FH mice. mice were exposed to different levels of environmental pathogens in the first 4 months, as housed in germ-free, specific pathogen–free, or conventional environments. In addition, wild-type C57BL/6J mice, mice, and FH mice were inoculated with cell wall extract (LCWE) mixed with complete Freund's adjuvant (CFA) at 2 months of age to develop a mouse model of IgA nephropathy.

Results: Elevated levels of human IgA1 in blood circulation and mucosal sites were observed in mice from exposure to pathogens. Compared with buffer-treated control mice, LCWE plus CFA-treated mice had moderately elevated levels of circulating human IgA1 (by one-fold) and human IgA1 immune complexes (by two-fold). Serum Gd-IgA1 levels increased four-fold after LCWE treatments. Analyses of the -glycopeptides of the IgA1 hinge region confirmed hypogalactosylation of IgA1, with the variety of the glycoforms matching those seen in clinical samples. Furthermore, LCWE induced persistent IgA1 and C3 deposition in the glomerular mesangial areas in association with mesangial expansion and hypercellularity, which are frequently observed in IgA nephropathy biopsies. The IGHA1FH mice stimulated with LCWE and CFA developed albuminuria and hematuria.

Conclusions: We observed elevated plasma Gd-IgA1 levels with kidney deposition of IgA1 in the mice after LCWE and CFA. In conjunction with factor H mutation, the mice exhibited severe glomerular alterations, associated with hematuria and albuminuria in resemblance of clinical IgA nephropathy.