Klein et al. contamination severity. These data were compiled statistically. The study considered epidemiological factors, the time from the end of the contamination, and contamination 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 Bax inhibitor peptide P5 is men and women above 39?years old. after a more severe infection. The titer of antibodies increases with time from the disease. Keywords: convalescent plasma, COVID\19, SARS\CoV\2, treatment Highlights The fastest increase of the antibodies level was observed up to 59 days after COVID\19. Higher levels of antibodies were found among people above the average age in both men and women. The antibodies level depend on the severity of the course of COVID\19 infection. The optimal group of plasma donors is men and women above 39 years old after a severe infection. 1.?INTRODUCTION The plasma of COVID19 convalescents is rich in anti\SARS\CoV\2 antibodies, and its use in the treatment of a severe course of this infection is widely accepted. Passive increasing of the body’s immune defense is based on multicenter observations of reduced mortality risk among transfused plasma patients with a high concentration of antibodies than those who received plasma with a low concentration of antibodies. Increased awareness of the health, society, and economy\connected harm?caused by COVID\19 and an increasing sense of solidarity led to the growing number of donating blood COVID\19 convalescent patients. 1 , 2 Determining the optimal group of donors and the optimal period for donation have considerable significance for preparing the plasma specimen. This study aims to determine the IgG anti\SARS\CoV\2 antibody titers in COVID\19 convalescents in the Pomeranian region of Poland, depending on the epidemiological factors, time since recovery (isolation), and the severity of the disease. 2.?MATERIALS AND METHODS We recruited COVID\19 convalescents (infection was confirmed by Polymerase chain reaction?[PCR]?analysis of nasal swabs) who reported donating blood at the Regional Center of Blood Donation and Treatment in Gdask (Poland). The inclusion criteria were: confirmed SARS\CoV\2 infection, 18C56 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 38C), fatigue, dyspnea, diarrhea, and smell/taste disturbances. The exclusion criteria were: autoimmune diseases, anti\HLA antibodies in the blood (postpregnancy or posttransfusion), active infection or Bax inhibitor peptide P5 oncological illness, history of viral disease (particularly HIV, Bax inhibitor peptide P5 Hepatitis B, and C), or infection with epidemic, Luck et al. noted that the plasma richest in antibodies was collected from convalescents 7C60 days after the end of infection symptoms. 4 Chen et al. reported a decrease in anti\SARS\CoV\2 IgG antibodies in the third month since recovery from COVID\19. 12 Klein et al. had similar results. 8 In our study, the convalescents had the recommended antibody titer (>1:500) after 30 days since the end of isolation. Our study participants donated plasma in various periods since recovery. Therefore, we had the opportunity to measure antibody titers for a long time, except for one male participant who donated blood 11 times within 6 months (due to continually high anti\SARS\CoV\2 titer, we could not obtain repeated antibody titer measurements in the same convalescent and asses individual trends. However, in this particular convalescent, it is not possible to exclude Mouse Monoclonal to Rabbit IgG (kappa L chain) the possibility of re\infection. In available literature is no widely available and generally agreed\upon best test for measuring neutralizing antibodies, and the antibody titers in convalescent plasma from patients who have recovered from COVID\19 are highly variable. 13 The level of 27.4?AU/ml (the result is the same as the level 1:500) was defined on the basis of research conducted by the Polish Nationality Center for Blood and Blood Treatment \ Maglumi and DiaSorin SARS\CoV\2 S\RBD IgG tests. 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 We first excluded anti\HLA antibodies (postpregnancy or post\transfusion) in all the collected blood samples, thus explaining the small number of female participants in our study. Furthermore, the weaker response to immunization, lack.