Immunoglobulin J chain

Immunoglobulin J chain (JCHAIN) is a 159-amino acid protein that serves a structural role in humoral immunity by linking monomer units of IgM or IgA immunoglobulins, facilitating polymerization of IgA and nucleation of IgM pentamers (UniProt: P01591). The protein also aids binding of these immunoglobulins to secretory component, functioning at the interface between adaptive immunity and mucosal protection. JCHAIN is expressed in antibody-secreting cells and tissues involved in immunoglobulin production and transport.

In the context of Alzheimer's Disease, JCHAIN is significantly upregulated in post-mortem AD brain tissue compared to age-matched controls (Chaparral AD proteomics). Proteomic analysis using tandem mass spectrometry across multiple subcellular fractions detected a mean log2 fold-change of +1.01, indicating elevated J chain levels in the AD brain. This upregulation may reflect altered immunological processes or neuroinflammatory responses characteristic of AD pathology, though the specific mechanistic contribution remains to be elucidated.