ABSTRACT
Abstract Human milk constitutes a secretion with unique functions of both nourishing the nursling and providing protection against enteric and respiratory infections, mainly due to its content of secretory IgA antibodies but also due to the presence of a plethora of bioactive factors. Specific IgA antibodies are produced locally by plasma cells derived from B lymphocytes that migrate from other mucosae to the mammary gland during lactation, particularly from the gastrointestinal and respiratory tracts. Therefore, here, the authors will provide a comprehensive review of the content and functions of different nutritional and bioactive anti-infectious components from breast milk, such as oligosaccharides, lactoferrin, haptocorrin, α-lactalbumin, k-casein, lysozyme, lactoperoxidase, mucin, fatty acids, defensins, cytokines and chemokines, hormones and growth factors, complement proteins, leukocytes and nucleic acids, including microRNAs, among many others, and the induction of antibody responses in breast milk after maternal vaccination with several licensed vaccines, including the anti-SARS-CoV-2 vaccine preparations used worldwide. Currently, in the midst of the pandemic, maternal vaccination has re-emerged as a crucial source of passive immunity to the neonate through the placenta and breastfeeding, considering that maternal vaccination can induce specific antibodies if performed during pregnancy and after delivery. There have been some reports in the literature about milk IgA antibodies induced by bacterial antigens or inactivated virus vaccines, such as anti-diphtheria-tetanus-pertussis, anti-influenza viruses, anti-pneumococcal and meningococcal polysaccharide preparations. Regarding anti-SARS-CoV-2 vaccines, most studies demonstrate elevated levels of specific IgA and IgG antibodies in milk with virus-neutralizing ability after maternal vaccination, which represents an additional approach to improve the protection of the nursling during the entire breastfeeding period.
ABSTRACT
Summary In the critical phase of immunological immaturity of the newborn, particularly for the immune system of mucous membranes, infants receive large amounts of bioactive components through colostrum and breast milk. Colostrum is the most potent natural immune booster known to science. Breastfeeding protects infants against infections mainly via secretory IgA (SIgA) antibodies, but also via other various bioactive factors. It is striking that the defense factors of human milk function without causing inflammation; some components are even anti-inflammatory. Protection against infections has been well evidenced during lactation against, e.g., acute and prolonged diarrhea, respiratory tract infections, including otitis media, urinary tract infection, neonatal septicemia, and necrotizing enterocolitis. The milk’s immunity content changes over time. In the early stages of lactation, IgA, anti-inflammatory factors and, more likely, immunologically active cells provide additional support for the immature immune system of the neonate. After this period, breast milk continues to adapt extraordinarily to the infant’s ontogeny and needs regarding immune protection and nutrition. The need to encourage breastfeeding is therefore justifiable, at least during the first 6 months of life, when the infant’s secretory IgA production is insignificant.
Resumo Na fase crítica de imaturidade imunológica do recém-nascido, em especial do sistema imune de mucosas, o lactente recebe grandes quantidades de componentes bioativos através do colostro e do leite materno. O colostro é o reforço imunológico natural mais potente conhecido pela ciência. O aleitamento materno protege o lactente de infecções principalmente por meio dos anticorpos IgA secretores (IgAS), mas também por meio de vários outros fatores bioativos. É surpreendente que os fatores de defesa do leite humano ajam sem causar inflamação e alguns componentes são, de fato, anti-inflamatórios. A proteção contra infecções tem sido bem evidenciada durante a lactação, combatendo, por exemplo, diarreia aguda e prolongada, infecções do trato respiratório, incluindo otite média, infecção do trato urinário, sepse neonatal e enterocolite necrosante. O conteúdo imunológico do leite evolui ao longo do tempo: nas fases iniciais de lactação, IgAS, fatores anti-inflamatórios e, mais provavelmente, as células imunologicamente ativas provêm ajuda adicional para o sistema imune imaturo do neonato. Depois desse período, o leite materno continua a adaptar-se extraordinariamente à ontogenia infantil, às suas necessidades de proteção imune e nutricionais. Entende-se, portanto, a necessidade de se estimular o aleitamento materno pelo menos durante o primeiro semestre de vida, período em que a produção própria de IgA secretória é ainda pouco significativa.