Diagnostic, prognostic, therapeutic and screening protocols

A method for determining gut wall integrity in a subject, the method comprising:

• (i) contacting a biological sample obtained from the subject with a polymeric Ig Receptor (pIgR) comprising in order from N-terminus to C-terminus a rabbit pIgR domain 1 and human pIgR domains 2 to 5, wherein the pIgR that binds to dimeric IgA antibody (dIgA) and forms a pIgR-dIgA complex, wherein the pIgR does not comprise a transmembrane domain,
• (ii) contacting the biological sample with a specific anti-Secretory IgA (SIgA) binding agent or anti-Secretory Component (SC) binding agent which binds to SiGa and forms an SigA-binding agent complex, and
• (iii) measuring a ratio of SigA2 of (ii) to dIgA2 of (i) and measuring a ratio of SIgA1 of (ii) to dIgA1 of (ii) wherein a ratio of SIgA2 to dIgA2 of >4 or a ratio of SIgA1 to dIgA1>10 is indicative of gut leakage and immune activation.

A method for detecting the presence of antigen-specific dimeric IgA antibody (dIgA) in a subject, the method comprising contacting a biological sample comprising antibodies obtained from a subject with a polymeric Ig Receptor (pIgR) comprising in order from N-terminus to C-terminus a rabbit pIgR domain 1 and human pIgR domaing 2 to 5, wherein the pIgR binds to dIgA, and measuring the level of antigen-specific dIgA bound to the pIgR, wherein the pIgR does not comprise a transmembrane domain, wherein the pIgR is bound to a solid support, wherein the subject has a condition selected from the group consisting of HIV, leprosy, syphilis, hepatitis, dengue virus, measles, and rubella, and wherein detection of the level of antigen-specific dIgA bound to the pIgR facilitates the selection of treatment for the condition.