# Profiling of Humoral Immune Response in Typhoid Patients against Differentially Extracted Whole Cell Bacterial Protein Derived from S. typhi and S. spp

## TL;DR

This study characterizes immune responses in typhoid patients using bacterial proteins from Salmonella typhi and related species to identify potential diagnostic biomarkers and vaccine targets.

## Contribution

The study identifies antigenic patterns recognized by different antibody isotypes in typhoid patients, offering new insights for diagnostics and vaccine development.

## Key findings

- Western blot analysis revealed distinct antigenic bands recognized by IgM, IgG, and IgA antibodies in typhoid patients.
- Three reactivity regions were identified, with the highest reactivity in proteins ≥55 kDa.
- The antigenic bands show potential as biomarkers for differentiating typhoid patients from carriers and healthy individuals.

## Abstract

Typhoid fever is a multiorgan infectious disease caused by Salmonella typhi. It is transmitted through fecal oral route and can be fatal without proper treatment. Therefore, early diagnosis of typhoid fever is crucial. In the previous study, we have developed TYPHOIDYNE EIA, which showed excellent synergy between the genus conserved and species-specific antigens in the serodiagnosis of typhoid fever. TYPHOIDYNE EIA can effectively detect and differentiate typhoid patients, typhoid vaccinated subjects, healthy subjects, and subjects with other febrile illnesses. Following the successful development of TYPHOIDYNE EIA, in this report, we further characterize the antigenic components of differentially extracted S. typhi and S. spp recognized by IgM, IgG, and IgA antibody isotypes in typhoid patients and possible typhoid carrier by the western blot (WB) assay. The WB characterization revealed a dynamic pattern of recognition, with significant variations in the number of antigenic bands observed between the differentially extracted arrays of antigens. The reactivity of patient's sera was divided into 3 regions, with region 1 (≥55 kDa) showing the strongest reactivity followed by region 2 (54 kDa–34 kDa) and region 3 (<34 kDa). Overall, the good synergy expressed in these bands suggests the potential role of these proteins in differentiating typhoid patients with possible typhoid carrier. The antigenic bands highlighted in this study are also identified as prospective biomarkers for diagnostic use and vaccine development.