BMC Infectious Diseases (Dec 2023)

Humoral and T cell responses to SARS-CoV-2 reveal insights into immunity during the early pandemic period in Pakistan

  • Kiran Iqbal Masood,
  • Shama Qaiser,
  • Syed Hani Abidi,
  • Erum Khan,
  • Syed Faisal Mahmood,
  • Areeba Hussain,
  • Zara Ghous,
  • Khekahsan Imtiaz,
  • Natasha Ali,
  • Muhammad Hasan,
  • Haris Ali Memon,
  • Maliha Yameen,
  • Shiza Ali,
  • Sadaf Baloch,
  • Gulzar Lakhani,
  • Paula M. Alves,
  • Najeeha Talat Iqbal,
  • Kumail Ahmed,
  • Junaid Iqbal,
  • Zulfiqar A. Bhutta,
  • Rabia Hussain,
  • Martin Rottenberg,
  • J. Pedro Simas,
  • Marc Veldhoen,
  • Kulsoom Ghias,
  • Zahra Hasan

DOI
https://doi.org/10.1186/s12879-023-08829-1
Journal volume & issue
Vol. 23, no. 1
pp. 1 – 14

Abstract

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Abstract Background Protection against SARS-CoV-2 is mediated by humoral and T cell responses. Pakistan faced relatively low morbidity and mortality from COVID-19 through the pandemic. To examine the role of prior immunity in the population, we studied IgG antibody response levels, virus neutralizing activity and T cell reactivity to Spike protein in a healthy control group (HG) as compared with COVID-19 cases and individuals from the pre-pandemic period (PP). Methods HG and COVID-19 participants were recruited between October 2020 and May 2021. Pre-pandemic sera was collected before 2018. IgG antibodies against Spike and its Receptor Binding Domain (RBD) were determined by ELISA. Virus neutralization activity was determined using a PCR-based micro-neutralization assay. T cell – IFN-γ activation was assessed by ELISpot. Results Overall, the magnitude of anti-Spike IgG antibody levels as well as seropositivity was greatest in COVID-19 cases (90%) as compared with HG (39.8%) and PP (12.2%). During the study period, Pakistan experienced three COVID-19 waves. We observed that IgG seropositivity to Spike in HG increased from 10.3 to 83.5% during the study, whilst seropositivity to RBD increased from 7.5 to 33.3%. IgG antibodies to Spike and RBD were correlated positively in all three study groups. Virus neutralizing activity was identified in sera of COVID-19, HG and PP. Spike reactive T cells were present in COVID-19, HG and PP groups. Individuals with reactive T cells included those with and without IgG antibodies to Spike. Conclusions Antibody and T cell responses to Spike protein in individuals from the pre-pandemic period suggest prior immunity against SARS-CoV-2, most likely from cross-reactive responses. The rising seroprevalence observed in healthy individuals through the pandemic without known COVID-19 may be due to the activation of adaptive immunity from cross-reactive memory B and T cells. This may explain the more favourable COVID-19 outcomes observed in this population.

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