The contribution of the antimicrobial activity of sIgA, lactoferrin, α-lactalbumin, serum albumin, and lysozyme to the total antimicrobial activity of serum was evaluated. 66 breast milk samples from healthy women aged from 23 to 45 years collected at different periods of lactation were studied. It was found that as the lactation period increased, not only the total antimicrobial activity (r = - 0.944) decreased, but also the activity of the low molecular weight fraction containing the sum of antimicrobial peptides (r = - 0.950). The median lactoferrin level varied from 3.46 mg/ml in colostrum to 0.94 mg/ml one year after the onset of lactation and correlated with serum activity (r = 0.616). The concentration of sIgA was maximal in the serum of colostrum (5.01 mg/ml) and significantly reduced in mature milk, remaining approximately at the same level in subsequent periods of lactation (1.0 mg/ml). Serum albumin concentration significantly decreased with increase of lactation period (from 5.52 to 4.68 mg/ml) and correlated with serum activity (r = 0.589). Evaluation of the effect of the purified α-lactalbumin on C. albicans cells in the range of 5-20 mg/ ml by spectrophotometry and microscopy showed the absence of fungicidal activity. At the same time, purified lactoferrin, IgA, lysozyme, and serum albumin demonstrated a direct fungicidal effect. The activity of the IgA preparation at a concentration relevant to the sIgA content in the serum of first day colostrum was 50.0%, and in the serum after 12 months - 31.0%; lactoferrin - 26.7% and 3.4%; serum albumin - 15.0% and 17.7%; lysozyme - 0.1% and 1.8%. Thus, the sum of the activities of these polypeptides at concentrations typical for the first-day colostrum was 91.7%, which is comparable to the total activity of this serum - 82.4%. The sum of the activities of these polypeptides, typical for 12 months of lactation, was 53.9%, and the total serum activity relevant to this period was 64.5%. Therefore, IgA and lactoferrin contribute the most significant antimicrobial activity in the serum of colostrum, whereas after 12 months of breastfeeding IgA and serum albumin become most significant.
We evaluated the effect of vaccination with anti-COVID-19 vaccine EpiVacCorona on serum antimicrobial activity, formation of specific IgG antibodies, and expression of some antimicrobial peptides. Antimicrobial activity of the serum from 55 volunteers towards S. aureus cells was measured spectrophotometrically; IgG-antibodies against SARS-CoV-2 antigen were assayed by ELISA; expression of genes encoding antimicrobial peptides LL37, HBD1, and HBD2 was evaluated by PCR with reverse transcription. Total antimicrobial serum activity and activity of its low-molecular-weight fraction containing antimicrobial peptides demonstrated an inverse correlation. Both activities after vaccination increased in case of low initial values, but decreased in case of high initial values. The vector of change of specific IgG antibodies to coronavirus inversely correlated with the vector of change of activity of antimicrobial peptide fraction. The expression of genes of antimicrobial peptides LL37, HBD1, and HBD2 looked like normal distribution depending on activities of the antimicrobial peptides in the corresponding sera.
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