key: cord-0715698-f6chnm48
authors: Skorek, Andrzej; Jaźwińska‐Curyłło, Anna; Romanowicz, Aleksandra; Kwaśniewski, Krzysztof; Narożny, Waldemar; Tretiakow, Dmitry
title: Assessment of anti‐SARS‐CoV‐2 antibodies level in convalescents plasma
date: 2021-11-09
journal: J Med Virol
DOI: 10.1002/jmv.27433
sha: 8146f93926f99fa3d7a613a1e78d0d6811866684
doc_id: 715698
cord_uid: f6chnm48

Despite extensive vaccination, the quantity of patients infected with the SARS‐CoV‐2 virus and its variants continues to grow worldwide. Treating patients with a severe course of COVID‐19 is a difficult challenge. One of the generally accepted and specific therapy methods is the use of plasma rich in anti‐SARS‐CoV‐2 antibodies. On the other hand, assessing the antibodies level depending on the time after infection allows for vaccine‐decision. The study marked the level of anti‐SARS‐CoV‐2 IgG antibodies in 351 COVID‐19 convalescent residents of one geographical region in Poland. The study group included blood donors. The studies were cross‐sectional and extended to a questionnaire to determine infection severity. These data were compiled statistically. The study considered epidemiological factors, the time from the end of the infection, and infection severity. The fastest increase of the antibodies level was observed up to 59 days after COVID‐19, and it was statistically significantly higher among men. Higher levels of antibodies were found among people above the average age in both men and women. There was an increase in the level of antibodies since the onset of the disease in men, while in women, it decreased. The antibodies level was also found to depend on the severity of the course of COVID‐19 infection. The optimal group of plasma donors in the studied geographical region is men and women above 39 years old. after a more severe infection. The titer of antibodies increases with time from the disease.

Polymerase chain reaction [PCR] analysis of nasal swabs) who reported donating blood at the Regional Center of Blood Donation and Treatment in Gdańsk (Poland). The inclusion criteria were: confirmed SARS-CoV-2 infection, 18-56 years of age, normal complete blood count (hemoglobin, hematocrit, erythrocyte, and leukocyte formula, platelets), normal blood pressure, pulse, and body temperature. In addition, the IgG anti-SARS-CoV-2 antibody titers were measured, and a detailed survey was conducted regarding symptoms such as chills, dry cough, musculoskeletal pain, conjunctivitis, fever (defined as ≥38°C), fatigue, dyspnea, diarrhea, and smell/taste disturbances. We divided the entire sample of participants into two subgroups depending on the severity of their COVID-19 illness. The severe course of COVID-19 was defined as ≥5 symptoms, whereas mild illness was defined as ≤4 symptoms.

Participation in our study was voluntary. It was conducted after the scheduled blood donation, whose purpose was to obtain plasma rich in anti-SARS-CoV-2 antibodies used to treat patients severely ill with COVID-19. Blood was collected 10-393 days after the 14-day isolation period. None of the participants had prior anti-SARS-CoV-2 vaccination, and none were hospitalized due to a severe course of COVID-19. Blood tests were performed using the MAGLUMI 800 device: test SARS-CoV-2 S-RBD IgG (Snibe Diagnostic; test result <1 AU/ml was nonreactive, whereas ≥1 AU/ml was reactive). Serological tests were performed using the in vitro chemiluminescent kit for the quantification of S-RBD IgG neutralizing antibodies (nAb) against SARS-CoV-2, intended for serum and plasma testing on automatic analyzers of the MAGLUMI series in accordance with the recommendations of the manufacturer of the SNIBE DIAGNOSTIC test. After collecting blood from the examined person, it was placed in test tubes with a separating gel or clot activator. After centrifugation (>10 000 RCF for 10 min), a sample (10 µl volume) containing no fibrin or other solids was collected. Then the sample, along with the buffer and magnetic particles coated with the recombinant S-RBD antigen, were mixed and incubated, which resulted in the formation of immune complexes. After magnetic field precipitation, the supernatant was removed and washed. After the addition of ABEI-labeled anti-human IgG antibodies, the sample was subjected to another incubation and precipitation followed by washing to remove unbound proteins from the sample. Finally, the chemiluminescence reaction was initiated and the light signals were measured with a photomultiplier for 3 s as a relative light unit (RLU) that is proportional to the SARS-CoV-2 S-RBD IgG concentration. All tests were performed after the manufacturer recommended calibration with quality control as well as precautions and safety measures for in vitro diagnostics. The sensitivity of the test (according to the manufacturer) in the case of a test performed 15 days after the onset of symptoms is 100.0% and its specificity is 99.6% (CE REF 30219017 M). 3 Our study protocol was approved by the local independent Bioethics Committee (NKBBN 199/2021). The obtained results were analyzed using the χ 2 test (Statistica 13.3 StatSoft Pl.).

Statistical significance was accepted at p < 0.05. Excel software was used to illustrate the obtained results and determine the trends (Microsoft Corporation).

We included a total of 351 COVID-19 convalescents in our study (305 males and 46 females), whose ages ranged from 18 to 63 (mean age 39). The obtained results were divided into four groups depending on the number of days since the isolation of the antibody titers (Table 1) .

We noted an increasing trend in anti-SARS-CoV-2 antibody titers depending on the time since infection (Table 1, Figure 1 ). The highest increase in the average antibody titer was observed in convalescents from Group I versus II (increase by 82,4%). In addition, we noted an increase of 27.1% between Group II and III and between III and IV 6.4%. The total increase in antibody titer between Group I versus IV was 146.6%.

Based on the mean or median age, the group of convalescents was divided into two groups: <39 and ≥39 years of age. The results were illustrated in Figure 2 . Participants who were at or above the mean age had higher antibody titers than those who were younger.

Among the older (≥39 lat years of age) participants, the line of the trend was increasing, whereas it was horizontal among the younger (<39) ones. We noted a statistically significant difference between the minimum and maximum values of antibody titers depending on age.

A similar correlation was noted in terms of sex. Average antibody titers were lower among females than among males (statistically significant difference p < 0.05). In addition, among the female participants, we noted a decrease in the antibody titers depending on the time since infection. In contrast, among the males, this correlation was positive (increasing titers, Figure 3 ).

We noted higher antibody titers among the male and female participants above the mean age (statistically significant difference, p < 0.05). In addition, among the male participants, the difference between anti-SARS-CoV-2 antibody titers increased with time since infection, whereas among the female participants, we observed an inverse correlation (Figures 4 and 5) .

We divided the entire sample of participants into two subgroups depending on the severity of their COVID-19 illness. The severe course of COVID-19 was defined as ≥5 symptoms, whereas mild illness was defined as ≤4 symptoms. We noted a difference in antibody titers' minimum and maximum values depending on the severity of illness ( Figure 6 ). These titers were higher among participants who The anti-SARS-CoV-2 antibody titers were the highest in males and females above the mean or median age (≥39 years of age) and

had a more severe course of COVID-19 (Figure 7) . It is noteworthy that in female participants, we noted the higher antibody titers only in the early period (<2-3 months since the end of isolation; Figure 5 ). severe course of COVID-19. However, others did not find a statistically significant influence of it on mortality. [8] [9] [10] [11] In Poland, the supply, production, and storage of plasma are conducted by Regional Centers of Blood Donation and Treatment.

Plasma donors are recruited from COVID-19 convalescents in whom high titers of specific anti-SARS-CoV-2 antibodies are expected. In our study, we noted higher antibody titers in convalescents who donated plasma later after infection, and these were mainly higher in those who were older and in males. These results are congruent with those published by Klein et al. 8 antibody titers is due to a more severe course of COVID-19 in older males and with higher mortality in that group. 16 Scully et al. sought to explain this difference via the influence of estrogen, testosterone, and progesterone on the immune response and the course of illness. 17 This correlation should also be considered as a possible explanation for the decreased antibody titers among older women in our study.

The presence of specific antibodies confirms past infection.

However, it remains unclear how effective they will be in other patients. In their study about Lassa fever, Jahrling et al. assessed the quality of plasma via specific IgG antibody titers and the neutralizing test. The authors noted that the most effective plasma was obtained from convalescents after 8 months since recovery and had high antibody and neutralizing test titers. 18 Our study similarly observed the convalescents should be used to treat severely ill patients in the region closest to where the plasma specimen was collected and prepared.

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