Humoral immune response to COVID-19 infection or vaccination among celiac disease patients

Introduction
Celiac disease (CD) is the most common autoimmune disease (AD) of the small intestine, affecting 1-2% of the population globally. It is characterized by the serological presence of autoantibodies (Abs), tissue transglutaminase antibody (tTGA), immunoglobulin (Ig) A, and IgG. Production of antibodies against SARS-CoV-2 after infection with the virus or vaccination is not well understood, especially among CD patients. The goal of this study was to measure the IgG antibodies in Jordanian patients infected with or vaccinated against the SARS-CoV-2 virus with different types of vaccines (Pfizer- BioNTech BNT162b2, Sinopharm BBIBP-CorV or Oxford-AstraZeneca ChAdOx1-S) and compare them with the levels in non-celiac controls. IgG levels induced by different vaccines were also compared.

Material and methods
The data for this cross-sectional study were obtained via a survey, whereby respondents were identified through convenience sampling. The healthy controls were given Questionnaire A while CD patients completed Questionnaire B. The blood samples from all participants were tested for the COVID-19 nucleocapsid protein (NP) IgG serum levels for participants previously infected with SARS-CoV-2, and spike (S) protein (S1/S2) IgG serum levels for vaccine recipients.

Results
The study involved 116 individuals, 60 (51.7%) of whom were CD patients. The NP IgG serum levels in the infected and S1/S2 IgG levels in the vaccinated CD patients were significantly lower than the levels in controls (48.3 ±44.5 vs. 81.1 ±34.4 and 49 ±45.8 vs. 75.7 ±38.6, p = 0.002). Moreover, only the Pfizer vaccine induced significantly more IgG antibodies in controls compared to CD patients (88.8 ±29.1 vs. 58.3 ±45.4, p = 0.01). On the other hand, the IgG levels were significantly higher in CD patients who received the Pfizer relative to the AstraZeneca vaccine (58.3 ±45.5 vs. 13.0 ±23.6, p = 0.03). After adjusting for presence of CD, age, sex, body mass index (BMI), comorbidities, vaccine type, smoking, gluten adherence, and time since infection or vaccination, SARS-CoV-2 S1/S2 IgG Abs and/or NP IgG Abs positivity was significantly associated with CD absence and negatively with vaccine type (AstraZeneca) with the odds ratios (ORs) of 9.6 (95% CI = 1.5-59.2, p = 0.015) and 0.03 (95% CI = 0.004-0.244. p = 0.001), respectively.

Conclusions
We concluded that patients with CD had lower SARS-CoV-2 S1/S2 IgG Abs and NP IgG Abs levels than controls, and CD patients who received the Pfizer vaccine had higher IgG levels than patients who received the AstraZeneca vaccine. We recommend that further research be conducted to address the dynamics of the antibody responses in CD patients regarding COVID-19 infection.