Abstract
From the moment we found out that the new infectious disease reported in Wuhan, China, now known as coronavirus disease 2019 (COVID-19), was actually caused by a coronavirus, questions about the future began to emerge. The waning of immunity against coronaviruses was not new and, therefore, was to also be expected in the case of this novel coronavirus infection in humans. Once we knew vaccines were indeed coming soon, we naturally began to wonder how the vaccine-induced immunity would stand up against a virus from a family known for their annual circulation.
By now severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has made its presence known in most corners of the world. Some regions have been fortunate to achieve high levels of vaccination and maintain relatively low levels of infection, but unfortunately, many other places have experienced the opposite. The major question now is around duration of the immune response elicited by natural infection or vaccination. The answers to these questions are starting to arrive now as we see that indeed, as expected, circulating antibody levels appear to decline in vaccinated or previously infected individuals. The next question is, what will that mean with respect to breakthrough infection, reinfection, and the need for additional booster shots?
Although many seem to be focused on antibody levels and their potential decline, others are reminding us that there is more to an immune response than just antibodies. Antibody levels are easy to measure and perhaps convenient to correlate with vaccine effectiveness, but real answers to questions regarding severity of breakthrough infection or reinfection may lie in the magnitude and stability of the cellular response.
In this issue, we have a number of articles pertaining to these and other related topics. A review by Ahsan et al. specifically addresses the role of adaptive immunity in protecting against reinfection. The authors also provide interesting discussion of T cell memory and cross-reactive immunity, as well as neutralizing antibodies and herd immunity. We also include a letter to the editor regarding a recent article on postinfectious immunity, as well as a subsequent response from the original authors.
Also on the topic of understanding cellular immunity against SARS-CoV-2 infection, a review by C. Huang explores the role of human monocytes and tissue macrophages, and their potential involvement in coronavirus pathogenesis with respect to interferon (IFN) responses and the cytokine storm. In line with this theme, Jiménez-Cotegana et al. provide data on the contribution of myeloid-derived suppressor cells versus regulatory T cells in the immunosuppression observed in COVID-19 patients.
Dysfunctional immune activation is common in many virus infections and remains to be an evolving story in the context of HIV infection. Skinner et al. describe a study in which they aimed to characterize the relationship between activated CD4+ T cell repertoire diversity and immune reconstitution after antiretroviral therapy in HIV-1/HCV coinfected individuals.
Let us also not forget that although many virologists and immunologists have joined the fight against SARS-CoV-2, many others continued to combat the viruses they had been studying for years, and some, of course, managed to do both. Razin et al. examined toll-like receptor (TLR) levels in HCV versus nonalcoholic fatty liver (NAFL) patients. Saikh and Ranji also provide new insights into TLR-ligand-induced signaling and discuss the potential for MyD88-targeted IFN induction.
To circle back to the topic of global prevalence and risk factors for infection, Copado-Villagrana et al. analyzed the prevalence of hepatitis A and E viruses in Mexico and concluded that the distribution of these viral infections varies throughout the year and among the country's geographical regions. Finally, in another seroprevalence study, Atewogbola et al. present interesting findings regarding risk factors for HIV seropositivity in pregnant women in Osun State, Nigeria.
In summary, the articles included in this issue highlight the multifactorial nature of the immune response against any virus and remind us of the importance of the interconnection between numerous components of the immune system and how they come together to determine the ultimate outcome of any infection.