Lactoferrin and SIgA Concentrations in Human Milk of SARS-CoV–Infected Mothers—Polish Cohort Study

<b>Background:</b> Human milk (HM) provides critical immunological support to neonates, serving as a key component of passive immunity during early life. <b>Objectives:</b> The main aim of this cohort study was to compare the concentrations of lactoferrin (Lf), secretory immunoglobulin A (SIgA), C-reactive protein (CRP), and their ratios to total protein levels in the colostrum of postpartum women infected with SARS-CoV-2 and healthy controls. <b>Methods:</b> Colostrum samples (3-5 mL) were collected from 40 mothers (20 infected, 20 healthy) during the first wave of the COVID-19 pandemic in Poland. Concentrations of Lf, SIgA, and CRP were analyzed using ELISA, and total protein content was measured using the bicinchoninic acid assay (BCA). <b>Results:</b> The presence of specific anti-SARS-CoV-2 SIgA antibodies was assessed via cassette serological lateral flow detection tests. Significant differences were observed in Lf (<i>p =</i> 0.04) and SIgA (<i>p =</i> 0.03) concentrations, both lower in the COVID-19 group. Lactoferrin medians were 12.30 g/L (infected) and 14.95 g/L (healthy), and for SIgA: 9.15 g/L vs. 15.01 g/L, respectively. No significant difference was found in CRP levels. Interestingly, the Lf/Protein ratio was significantly higher in the infected group (<i>p</i> = 0.03), whereas the SIgA/Protein ratio did not differ. Furthermore, 75% of infected mothers had positive anti-SARS-CoV-2 SIgA results. These mothers also showed a higher Lf/Protein ratio. Among healthy controls, 90% had negative test results. <b>Conclusions:</b> These findings suggest a potential compensatory role of lactoferrin in the nonspecific immune response to SARS-CoV-2, though stress-related reductions in SIgA levels cannot be excluded.