Claudio Rodríguez-Camejo

Hypoprolactinemia (hypoPRL) disrupts lactation and compromises milk production. Although maternal milk is a critical source of nutrients and bioactive compounds for newborns, the consequences of deficient lactation based on reduced milk quantity on the offspring’s immune development remain incompletely understood. Therefore, this study aimed to elucidate how deficient lactation due to hypoPRL interferes with offspring immunity and development. Female Sprague Dawley (SD) and spontaneous hypoPRL Oncins France Colony A (OFA) rats were euthanized on day 2 of lactation to assess the impact of hypoPRL on serum, milk, and tissue samples. We demonstrated that early deficient lactation in the OFA model impaired maternal performance, leading to increased pup mortality during early lactation. OFA pups exhibited reduced body weight and weight gain, decreased cerebral weight and index, and an increased cephalization index. Thymic development was markedly altered, as evidenced by reduced thymus weight, area, and cortical extension. These structural changes were accompanied by increased thymic Rag 1 expression, suggesting altered lymphocyte development. In parallel, passive immune transfer was compromised, with reduced levels of OVA-specific immunoglobulin isotypes detected in pup serum, reflecting changes in milk-derived immune support. In summary, maternal hypoPRL during early lactation adversely affects offspring growth and thymic maturation with lasting consequences for neonatal immune maturation. This study provides a novel experimental framework to investigate the consequences of lactation deficiency with potential implications for understanding lactation insufficiency and its impact on neonatal immune exposure.

Human milk (HM) constitutes the first immunological barrier and the main source of nutrients and bioactive components for newborns. Immune factors comprise up to 10% of the protein content in HM, where antibodies are the major components (mainly IgA, IgG, and IgM). In addition, antibacterial enzymes such as lysozyme and immunoregulatory factors such as soluble cluster of differentiation 14 (sCD14) and transforming growth factor β2 (TGF-β2) are also present and play important roles in the protection of the infant's health. Donor milk processed in HM banks by Holder pasteurization (HoP; 62.5°C, 30 min) is a safe and valuable resource for preterm newborns that are hospitalized, but is reduced in major immunological components due to thermal inactivation. We hypothesized that high hydrostatic pressure (HHP) and high-pressure homogenization (HPH) are 2 processes that can be used on HM to reduce total bacteria counts while retaining immunological components. We studied the effects of HHP (400, 450, and 500 MPa for 5 min applied at 20°C) and HPH (200, 250, and 300 MPa, milk inlet temperature of 20°C) applied to mature HM, on microbiological and immunological markers (IgA, IgG, IgM, sCD14, and TGF-β2), and compared them with those of traditional HoP in HM samples from healthy donors. The HHP processing between 400 and 500 MPa at 20°C reduced counts of coliform and total aerobic bacteria to undetectable levels (<1.0 log cfu/mL) while achieving approximately 100% of immunological component retention. In particular, comparing median percentages of retention of immunological components for 450 MPa versus HoP, we found 101.5 versus 50.5% for IgA, 89.5 versus 26.0% for IgM, 104.5 versus 75.5% for IgG, 125.0 versus 72.5% for lysozyme, 50.6 versus 0.1% for sCD14, and 88.5 versus 61.1% for TGF-β2, respectively. Regarding HPH processing, at a pressure of 250 MPa and inlet temperature of 20°C, the process showed good potential to reduce coliforms to undetectable levels and total aerobic bacteria to levels slightly above those obtained by HoP. The median percentages of retention of immunological markers for HPH versus HoP were 71.5 versus 52.0%, 71.0 versus 27.0%, 104.0 versus 66.5%, and 30.9 versus 0.2%, for IgA, IgM, IgG, and sCD14, respectively; results did not significantly differ for lysozyme and TGF-β2. The HPH at 300 MPa produced higher inactivation of immunological components, similar to values achieved with HoP.