Humoral immunity for durable control of SARS-CoV-2 and its variants

Anti_spike and anti_nucleocapsid IgG responses to SARS-CoV-2 in children of Jordan

Background

It is proven that children have significantly milder COVID-19 disease compared to adults. Various immunological characteristics influence this age-related difference in protection against COVID-19. Pediatric COVID-19 in Jordan is extremely under reported.

Objectives

The primary goal of this work is to identify the anti_S and anti_N antibody responses in a random group of children in Jordan and compare it to that of naturally infected-unvaccinated adults.

Methods

151 unvaccinated children, 4 days to 18 years old, were screened for anti_S and anti_N antibodies. History of COVID-19 infection or exposure to infection and symptom severity were reported by parents on a special questionnaire.

Results

78.9 % and 65.3 % of participants were seropositive for anti_S IgG and anti_N Abs, respectively. There was a remarkable association between age and anti_S IgG and anti_N IgG antibody titers, as children aged 12 years or older had increased anti_S IgG titers (mean = 19.3 BAU/mL) compared to younger groups (means of 10.15, 9.24, 7.91 BAU/mL for age groups 6-12, 1-6, less than 1 year, respectively). Gender did not show a statistically important role in anti_S and anti_N IgG seropositivity rates or titers. Children displayed significantly elevated anti_S titers (mean = 13.23 BAU/mL) compared to naturally infected adults (mean = 9.72 BAU/mL), in contrast, adults' anti_N titers (mean = 39.64 U/mL) were significantly higher compared to those of children (mean = 10.77 U/mL).

Conclusions

The current work provides evidence of distinctly robust and persistent humoral immunity displayed by high anti_S and anti_N IgG in children, even >12 months post-infection. Age was the only factor that had a significant statistical impact on anti_S and anti_N Ab levels among the pediatric group in this study. Children exhibited significantly higher anti_S titers than naturally infected adults. In contrast, adults' anti_N titers were significantly higher. Such information can assist direct pediatric SARS-CoV-2 immunization programs, with implications for creating age-targeted strategies for diagnostic and population protection measures.

B cell responses to SARS-CoV-2

This chapter provides an overview of B cell responses in COVID-19, highlighting the structure of SARS-CoV-2 and its impact on B cell immunity. It explores the production and maturation of SARS-CoV-2-specific B cells, with a focus on the two distinct phases of the humoral immune response: the extrafollicular (EF) phase and the germinal center (GC) phase. Furthermore, the interplay between B cells, follicular T helper cells, CD4+ T cells, and plasma cells is discussed, emphasizing their collaborative role in mounting an effective humoral immune response against SARS-CoV-2. The concept of immunological memory is explored, highlighting the roles of plasma cells and B memory cells in providing long-term protection. The chapter delves into the antibody response during SARS-CoV-2 infection, categorizing the types of antibodies generated. This includes a detailed analysis of neutralizing antibodies, such as those directed against the receptor-binding domain (RBD) and the N-terminal domain (NTD), as well as non-neutralizing antibodies. The role of mucosal antibodies, cross-reactive antibodies, and auto-reactive antibodies is also discussed. Factors influencing the dynamics of anti-SARS-CoV-2 antibodies are examined, including the duration and strength of the humoral response. Additionally, the chapter highlights the impact of the Omicron variant on humoral immune responses and its implications for vaccine efficacy and antibody-mediated protection.

Humoral Response Kinetics and Cross-Immunity in Hospitalized Patients with SARS-CoV-2 WT, Delta, or Omicron Infections: A Comparison between Vaccinated and Unvaccinated Cohorts

With the ongoing evolution of severe acute respiratory virus-2 (SARS-CoV-2), the number of confirmed COVID-19 cases continues to rise. This study aims to investigate the impact of vaccination status, SARS-CoV-2 variants, and disease severity on the humoral immune response, including cross-neutralizing activity, in hospitalized COVID-19 patients. This retrospective cohort study involved 122 symptomatic COVID-19 patients hospitalized in a single center. Patients were categorized based on the causative specific SARS-CoV-2 variants (33 wild-type (WT), 54 Delta and 35 Omicron) and their vaccination history. Sequential samples were collected to assess binding antibody responses (anti-S/RBD and anti-N) and surrogate virus neutralization tests (sVNTs) against WT, Omicron BA.1, and BA.4/5. The vaccinated breakthrough infection group (V) exhibited higher levels of anti-S/RBD compared to the variant-matched unvaccinated groups (UVs). The Delta infection resulted in a more rapid production of anti-S/RBD levels compared to infections with WT or Omicron variants. Unvaccinated severe WT or Delta infections had higher anti-S/RBD levels compared to mild cases, but this was not the case with Omicron infection. In vaccinated patients, there was no difference in antibody levels between mild and severe infections. Both Delta (V) and Omicron (V) groups showed strong cross-neutralizing activity against WT and Omicron (BA.1 and BA.4/5), ranging from 79.3% to 97.0%. WT (UV) and Delta (UV) infections had reduced neutralizing activity against BA.1 (0.8% to 12.0%) and BA.4/5 (32.8% to 41.0%). Interestingly, patients who received vaccines based on the ancestral spike exhibited positive neutralizing activity against BA.4/5, even though none of the study participants had been exposed to BA.4/5 and it is antigenically more advanced. Our findings suggest that a previous vaccination enhanced the humoral immune response and broadened cross-neutralizing activity to SARS-CoV-2 variants in hospitalized COVID-19 patients.

Modeling the sequence dependence of differential antibody binding in the immune response to infectious disease

Past studies have shown that incubation of human serum samples on high density peptide arrays followed by measurement of total antibody bound to each peptide sequence allows detection and discrimination of humoral immune responses to a variety of infectious diseases. This is true even though these arrays consist of peptides with near-random amino acid sequences that were not designed to mimic biological antigens. This "immunosignature" approach, is based on a statistical evaluation of the binding pattern for each sample but it ignores the information contained in the amino acid sequences that the antibodies are binding to. Here, similar array-based antibody profiles are instead used to train a neural network to model the sequence dependence of molecular recognition involved in the immune response of each sample. The binding profiles used resulted from incubating serum from 5 infectious disease cohorts (Hepatitis B and C, Dengue Fever, West Nile Virus and Chagas disease) and an uninfected cohort with 122,926 peptide sequences on an array. These sequences were selected quasi-randomly to represent an even but sparse sample of the entire possible combinatorial sequence space (~1012). This very sparse sampling of combinatorial sequence space was sufficient to capture a statistically accurate representation of the humoral immune response across the entire space. Processing array data using the neural network not only captures the disease-specific sequence-binding information but aggregates binding information with respect to sequence, removing sequence-independent noise and improving the accuracy of array-based classification of disease compared with the raw binding data. Because the neural network model is trained on all samples simultaneously, a highly condensed representation of the differential information between samples resides in the output layer of the model, and the column vectors from this layer can be used to represent each sample for classification or unsupervised clustering applications.