# Investigating Associations between HLA-DR Genotype, H. pylori Infection, and Anti-CagA IgA Seropositivity in a Turkish Gastritis Cohort

## TL;DR

This study explores how HLA-DR genotypes influence immune responses to H. pylori infection and CagA antibodies in a Turkish gastritis cohort.

## Contribution

The study identifies HLA-DRB1 alleles associated with susceptibility or protection against H. pylori and CagA immunity.

## Key findings

- HLA-DRB1*11:04 is linked to increased H. pylori infection and reduced anti-CagA IgA.
- HLA-DRB1*03:01 is associated with higher anti-CagA IgA and better CagA peptide presentation.
- In silico analysis shows DRB1*03:01 presents more CagA peptides than DRB1*11:04.

## Abstract

Helicobacter pylori (H. pylori) is associated with gastric inflammation and mucosal antibodies against its cytotoxin-associated gene A (CagA) are protective. Vaccine-elicited immunity against H. pylori requires MHC class II expression, indicating that CD4+ T cells are protective. We hypothesized that the HLA-DR genotypes in human populations include protective alleles that more effectively bind immunogenic CagA peptide fragments and susceptible alleles with an impaired capacity to present CagA peptides. We recruited patients (n = 170) admitted for gastroendoscopy procedures and performed high-resolution HLA-DRB1 typing. Serum anti-CagA IgA levels were analyzed by ELISA (23.2% positive) and H. pylori classified as positive or negative in gastric mucosal tissue slides (72.9% positive). Pearson Chi-square analysis revealed that H. pylori infection was significantly increased in DRB1*11:04-positive individuals (p = 0.027). Anti-CagA IgA was significantly decreased in DRB1*11:04 positive individuals (p = 0.041). In contrast, anti-CagA IgA was significantly increased in DRB1*03:01 positive individuals (p = 0.030). For these HLA-DRB1 alleles of interest, we utilized two in silico prediction methods to compare their capacity to present CagA peptides. Both methods predicted increased numbers of peptides for DRB1*03:01 than DRB1*11:04. In addition, both alleles preferred distinctively different CagA 15mer peptide sequences for high affinity binding. These observations suggest that DRB1*11:04 is a susceptible genotype with impaired CagA immunity, whereas DRB1*03:01 is a protective genotype that promotes enhanced CagA immunity.