Expression of immunoglobulin G in human podocytes, and its role in cell viability and adhesion

Podocyte injury occurs during the initiation and development of numerous forms of glomerular disease, and antibodies targeting podocytes have become a biomarker for diagnosis and monitoring treatment response. Accumulating evidence has suggested that immunoglobulin (Ig) is expressed in non-B lineage cells, including epithelial cancer cells, myeloid cells and several types of normal cells. The main aim of the present study was to ascertain the expression of IgG in human podocytes and to determine its potential role in cellular bioactivity. The present study detected positive staining for IgG heavy chain (Igγ) and its subtype γ4, and the light chains κ and λ in the cytoplasm or on the membrane by immunofluorescence. In addition, positive bands were detected for Igγ, γ1, γ3, γ4, κ and λ in the lysates of a podocyte cell line by western blotting. Mass spectrometry confirmed IgG1 as an intact tetramer in the culture supernatant. Constant region transcripts of Igγ, γ1, γ3, γ4, κ and λ were identified by reverse transcription-polymerase chain reaction, and DNA sequencing of these transcripts revealed 96–99% similarity with Ig mRNAs in the National Center for Biotechnology Information database. Compared with the diverse gene rearrangements from B cell-derived Ig, podocyte-derived Ig exhibited conservative V(D)J patterns in the variable regions of Igγ and κ chains. Furthermore, the present study investigated the mechanism underlying IgG production in these cells by examining the expression of recombination activating gene (RAG)1, RAG2 and activation-induced cytidine deaminase. The expression levels of these proteins suggested that podocyte-derived Ig and traditional Ig may be generated in a similar manner. Furthermore, small interfering RNA-mediated downregulation of IgG expression reduced podocyte viability and adhesive capabilities. These findings suggested that IgG is expressed in podocytes and that this expression may be associated with podocyte function. Due to its potential biological and clinical significance, this phenomenon warrants further investigation.