Antibody Profile of Colostrum and the Effect of Processing in Human Milk Banks: Implications in Immunoregulatory Properties

[Pregnancy and breastfeeding in women with multiple sclerosis]

The diagnosis of multiple sclerosis (MS) in women of reproductive age is associated with many uncertainties regarding childbearing and lactation. Pregnancies of MS patients are not usually considered high-risk pregnancies per se. The likelihood of pregnancy complications or adverse pregnancy outcomes is not increased by the disease; however, a careful planning of pregnancy is important in order to choose the treatment option with the greatest benefit for the mother and the least possible risk for the baby. For highly active courses of the disease, anti-CD20 antibodies, cladribine, or continued administration of natalizumab show the best data. Patients with MS can be supported in their desire to breastfeed. If women have had a very active disease course, it is recommended that treatment should be started as soon as possible postpartum. Interferon-beta preparations, glatiramer acetate and ofatumumab are also approved for use during breastfeeding but off-label breastfeeding is also possible with other monoclonal antibodies.

Effects of human donor milk on gut barrier function and inflammation: in vitro study of the beneficial properties to the newborn

Introduction

The gastrointestinal and immune systems of premature infants are not fully developed, rendering them more vulnerable to severe complications like necrotizing enterocolitis. Human milk offers a rich array of bioactive factors that collectively contribute to reducing the incidence of gut infections and inflammatory conditions. When a mother's milk is unavailable, preterm infants are often provided with donor human milk processed in Human Milk Banks. However, it remains uncertain whether pasteurized milk confers the same level of risk reduction as unprocessed milk. This uncertainty may stem from the well-documented adverse effects of heat treatment on milk composition. Yet, our understanding of the comprehensive impact on protective mechanisms is limited.

Methods

In this study, we conducted a comparative analysis of the effects of raw versus pasteurized milk and colostrum versus mature milk on cellular functions associated with the gut epithelial barrier and responses to inflammatory stimuli. We utilized THP-1 and HT-29 cell lines, representing monocyte/macrophages and gut epithelial cells, respectively.

Results

Our observations revealed that all milk types stimulated epithelial cell proliferation. However, only raw colostrum increased cell migration and interfered with the interaction between E. coli and epithelial cells. Furthermore, the response of epithelial and macrophage cells to lipopolysaccharide (LPS) was enhanced solely by raw colostrum, with a milder effect observed with mature milk. In contrast, both raw and pasteurized milk diminished the LPS induced response in monocytes. Lastly, we examined how milk affected the differentiation of monocytes into macrophages, finding that milk reduced the subsequent inflammatory response of macrophages to LPS.

Discussion

Our study sheds light on the impact of human milk on certain mechanisms that potentially account for its protective effects against necrotizing enterocolitis, highlighting the detrimental influence of pasteurization on some of these mechanisms. Our findings emphasize the urgency of developing alternative pasteurization methods to better preserve milk properties. Moreover, identifying the key components critically affected by these protective mechanisms could enable their inclusion in donor milk or formula, thereby enhancing immunological benefits for vulnerable newborns.

Anti-CD20 therapies in pregnancy and breast feeding: a review and ABN guidelines

Neurologists increasingly use anti-CD20 therapies, including for women of childbearing age, despite these medications being unlicensed for use in pregnancy. Current evidence suggests that women can safely conceive while taking anti-CD20 therapy. Women should not be denied treatment during pregnancy when it is clinically indicated, although they should be counselled regarding live vaccinations for their infant. Women receiving regular ocrelizumab for multiple sclerosis should preferably wait 3 months before trying to conceive. There are few data around ofatumumab in pregnancy, and while there is probably a class effect across all anti-CD20 therapies, ofatumumab may need to be continued during pregnancy to maintain efficacy. We recommend that anti-CD20 therapies can be safely given while breast feeding. It is important to make time to discuss treatments with women of childbearing age to help them choose their most suitable treatment. Outcomes should be monitored in pregnancy registries.

Comparative Detection of Immunoglobulin Isotypes and Subclasses against Toxoplasma gondii Soluble Antigen in Serum and Colostrum Samples from Puerperal Women

Background: Toxoplasma gondii is an obligate intracellular parasite that can infect several species, including humans, and can cause severe damage to the fetus when the infection occurs during pregnancy. The environment and/or food contamination are critical to spreading the infection. Human milk is rich in nutrients and bioactive elements that provide growth and development of the immune system of the newborn. All isotypes of immunoglobulins are present in human colostrum and they are produced from systemic or local sources. Breastfeeding protects the infant against various pathogens, but there is no conclusive study to detect IgG subclasses in colostrum against T. gondii. Therefore, the aim of this study was to detect and evaluate the presence of antibody isotypes against T. gondii in paired samples of serum and colostrum. Methods: The study included 283 puerperal patients. ELISA (Enzyme-Linked Immunosorbent Assay) for detection of anti-T. gondii-specific IgM, IgA, and IgG isotypes and IgG1, IgG3, and IgG4 subclasses were conducted on paired samples of serum and colostrum. Results: It was found that 45.9%, 6.0%, and 2.1% of serum samples and 45.2%, 7.1%, and 2.1% of colostrum samples were positive for IgG, IgM, and IgA, respectively. Specific IgG1, IgG3, and IgG4 were positive, respectively, in 98.5%, 54.6%, and 44.6% of serum samples, in contrast with 56.9%, 78.5%, and 34.6% of colostrum samples. Thus, the predominant reactivity of IgG subclasses against T. gondii was IgG1 in serum and IgG3 in colostrum. The higher percentage of positive samples and higher levels of anti-T. gondii IgG3 antibodies were observed in colostrum, when compared to serum samples, suggesting a local production of this subclass. IgG3 and IgG1 subclasses presented different percentages of positivity in serum and colostrum. Only the IgG1 subclass showed a significant correlation between the levels of anti-T. gondii in serum and colostrum, suggesting that IgG1 in breast milk comes from a systemic source. IgG4 showed a similar percentage of positivity in both sample types, but no significant correlation was observed between their levels. Conclusion: Colostrum presents representative levels of IgM, IgA, IgG1, IgG3, and IgG4 antibodies specific to T. gondii. The detection of these antibodies presents the potential for diagnostic application of colostrum samples to better identify the diagnostic status of T. gondii infection, especially during the acute phase. In addition, breastfeeding can also be a possible source of protective antibodies for the newborn against toxoplasmosis, an anthropozoonosis maintained by environmental infection, which interferes in the public health of many countries.

[Current aspects of antirheumatic therapy in pregnancy planning, during pregnancy and breastfeeding]

Active rheumatic disease is a known factor for increased fetomaternal risks during pregnancy. Remission or inactive disease should therefore be targeted to reduce these risks by using pregnancy-compatible antirheumatic drugs as recommended by international guidelines. Teratogenic antirheumatic drugs, such as mycophenolate, methotrexate, cyclophosphamide and thalidomide should be stopped about 3 months prior to conception. Leflunomide is a weak human teratogen that should be stopped and eliminated with cholestyramine prior to conception. Furthermore, drugs with limited data, such as apremilast and JAK inhibitors as well as new biologics should be avoided during gestation. Pregnancy-compatible drugs are the antirheumatic drugs hydroxychloroquine, sulfasalazine, azathioprine, cyclosporine, tacrolimus, colchicine, non-selective NSAIDs, low-dose prednisone/prednisolone and TNF inhibitors. These drugs as well as other biologics, such as rituximab can be used during lactation. In a preconception counselling visit, the benefits and the international recommendations of pregnancy-compatible antirheumatic drugs should be discussed with the patient and be weighed against the possible fetomaternal risks of an active disease to enable a shared decision-making.

Drug and Neurofilament Levels in Serum and Breastmilk of Women With Multiple Sclerosis Exposed to Natalizumab During Pregnancy and Lactation

Objective

To determine the transfer of the monoclonal antibody natalizumab into breastmilk and to evaluate drug and serum neurofilament light chain ((s)NfL) levels in natalizumab exposed pregnancies and lactation periods.

Methods

Eleven women with relapsing remitting multiple sclerosis treated with natalizumab during pregnancy and lactation were included in this study. Breastmilk samples were collected up to 302 days after delivery and analyzed for natalizumab concentration and NfL. Additionally, maternal drug levels and sNfL were determined preconceptually, in each trimester, at delivery and postpartum. Clinical and radiological disease activity was systemically assessed across pregnancy and postpartum period.

Results

The mean average natalizumab concentration in breast milk was low at 0.06 µg/ml [standard deviation (SD) 0.05] in the eight patients who provided serial breastmilk samples with an estimated mean absolute infant dose of 0.007 mg/kg/d (SD 0.005). The relative infant dose (RID), a metric comparing the infant with maternal drug exposure was low as well with a mean of 0.04% (SD=0.03). Most patients had a maximum concentration in breast milk at one to eight days after infusion. Pregnancy was associated with a non-significant decline of the median natalizumab serum concentration. All patients exposed to natalizumab prior (n=10) and during pregnancy (n=11) kept free of disease activity during gestation. While pregnancy was associated with low sNfL levels in patients treated with natalizumab prior and during pregnancy, the postpartum period was linked to a transient sNfL increase in some patients without any evidence of clinical or radiological disease activity. NfL was detectable in the majority of breastmilk samples with a median concentration of 1.7 pg/ml (range 0.004-18.1).

Conclusion

We determined transfer of natalizumab into breastmilk with an RID far below the threshold of concern of 10%. Studies including childhood development assessment are needed in order to gain safety data about natalizumab-exposed breastfeeding. SNfL assessment might be a useful adjunct to monitor silent disease activity and therapeutic response during pregnancy and postpartum period. However, further investigations regarding transient postpartum sNfL increases are required to determine its association to parturition per se or to a silent disease activity in people with multiple sclerosis.

Rituximab and Canakinumab Use During Lactation: No Detectable Serum Levels in Breastfed Infants

Introduction

In breastfeeding patients with chronic inflammatory rheumatic diseases, a postpartum flare may require the use of biologics. However, data on the safety of biologics during lactation are scarce, potentially impeding the decision-making process.

Case series

We report two cases of women in whom treatment with a monoclonal IgG antibody (rituximab or canakinumab) was indicated during the lactation period. In both cases, breastfeeding was continued, and drug levels in the mother’s serum, in serial breast milk samples and in the infant’s serum were measured. Both rituximab and canakinumab showed minimal drug concentrations in breast milk and no detectable levels in the infants’ sera.

Conclusion

The lack of detectable levels of rituximab and canakinumab in the sera of breastfed infants reflects the poor oral bioavailability of these biologics and helps to promote their use in breastfeeding patients.

Immune profiling of breast milk from mothers with treated celiac disease

BACKGROUND

The protective effect of breastfeeding on celiac disease (CD) onset is controversial. We studied a wide range of milk components in milk produced by celiac mothers following long-term gluten-free diet (GFD) in comparison to milk produced by healthy mothers.

METHODS

Breast-milk samples from celiac (n = 33) and healthy (n = 41) mothers were obtained during the first year of lactation. A panel of bioactive components was analyzed by enzyme-linked immunosorbent assay in the aqueous fraction. We studied molecules involved in defenses, immunoregulation, and strengthening of the gut-epithelial barrier.

RESULTS

During late lactation (from 6 to 12 months after delivery), the content of total immunoglobulin A (IgA) and IgM was significantly lower in the milk produced by celiac patients. Nevertheless, gliadin (GFD)-specific IgA relative contribution was higher in this group, in contrast to tetanus toxoid-specific antibodies. The balance between pro-inflammatory and anti-inflammatory molecules was different. While interleukin-6, tumor necrosis factor-α, and monocyte chemoattractant protein-1 were most frequently found in samples from celiac mothers, soluble Toll-like receptor-2 prevalence was lower.

CONCLUSIONS

We describe differences between the innate and adaptive immune profile of milk produced by celiac and healthy mothers. These results might explain previous controversial reports about breastfeeding and CD protection.

IMPACT

In spite of a long-term adherence to GFD, the milk produced by mothers with CD exhibit a different immune profile, in relation with some immunoregulatory factors and antibody content. This work shows a more comprehensive characterization of milk from celiac mothers, including macronutrients, lysozymes, growth factors, and immunoregulatory components that had not been studied before. The present study widens the available data regarding the characteristics of human milk of celiac mothers following GFD. Further follow-up studies of the health of children who were breastfed by celiac mothers will be necessary in order to also estimate the impact of the present results therein.

Transfer of monoclonal antibodies into breastmilk in neurologic and non-neurologic diseases

OBJECTIVE

To review currently available data on the transfer of monoclonal antibodies (mAbs) in the breastmilk of women receiving treatment for neurologic and non-neurologic diseases.

METHODS

We systematically searched the medical literature for studies referring to 19 selected mAb therapies frequently used in neurologic conditions and "breastmilk," "breast milk," "breastfeeding," or "lactation." From an initial list of 288 unique references, 29 distinct full-text studies met the eligibility criteria. One additional study was added after the literature search based on expert knowledge of an additional article. These 30 studies were reviewed. These assessed the presence of our selected mAbs in human breastmilk in samples collected from a total of 155 individual women.

RESULTS

Drug concentrations were typically low in breastmilk and tended to peak within 48 hours, although maximum levels could occur up to 14 days from infusion. Most studies did not evaluate the breastmilk to maternal serum drug concentration ratio, but in those evaluating this, the highest ratio was 1:20 for infliximab. Relative infant dose, a metric comparing the infant with maternal drug dose (<10% is generally considered safe), was evaluated for certolizumab (<1%), rituximab (<1%), and natalizumab (maximum of 5.3%; cumulative effects of monthly dosing are anticipated). Importantly, a total of 368 infants were followed for ≥6 months after exposure to breastmilk of mothers treated with mAbs; none experienced reported developmental delay or serious infections.

CONCLUSIONS

The current data are reassuring for low mAb drug transfer to breastmilk, but further studies are needed, including of longer-term effects on infant immunity and childhood development.

More than sugar in the milk: human milk oligosaccharides as essential bioactive molecules in breast milk and current insight in beneficial effects

Human milk is the gold standard for newborn infants. Breast milk not only provides nutrients, it also contains bioactive components that guide the development of the infant's intestinal immune system, which can have a lifelong effect. The bioactive molecules in breast milk regulate microbiota development, immune maturation and gut barrier function. Human milk oligosaccharides (hMOs) are the most abundant bioactive molecules in human milk and have multiple beneficial functions such as support of growth of beneficial bacteria, anti-pathogenic effects, immune modulating effects, and stimulation of intestine barrier functions. Here we critically review the current insight into the benefits of bioactive molecules in mother milk that contribute to neonatal development and focus on current knowledge of hMO-functions on microbiota and the gastrointestinal immune barrier. hMOs produced via genetically engineered microorganisms are now applied in infant formulas to mimic the nutritional composition of breast milk as closely as possible, and their prospects and scientific challenges are discussed in depth.

Impact of Holder pasteurization on immunological properties of human breast milk over the first year of lactation

BACKGROUND

The timing of milk donations to human milk banks ranges from a few days to more than 1 year after delivery, and the Holder method is used for pasteurization. We evaluated the effect of temporal variation and thermal treatment on the immunological properties of milk.

METHODS

We analyzed 73 milk samples, raw and after pasteurization, donated at different lactation stages. We studied antibodies, lysozyme, cytokines, soluble receptors, and factors with impact on barrier function. We also evaluated in vitro the capacity of milk to modulate nuclear factor-κB (NF-κB) signaling in an HT-29 epithelial cell line stimulated with tumor necrosis factor-α (TNF-α).

RESULTS

With few exceptions, immune components exhibited their highest levels in colostrum, and were stable in the various stages of mature milk. Pasteurization altered the immunological composition of milk, and very drastically for some components. Raw milk of the first year reduced NF-κB activation in HT-29 cells treated with TNF-α to approximately the same extent, and Holder pasteurization significantly affected this capacity.

CONCLUSIONS

Overall, the present work reports that mature donated milk is equally valuable over the first year of lactation, but warns about drastic losses of anti-inflammatory properties during Holder pasteurization that could be critical for the health of preterm infants.

Maternal and Neonatal Hair Cortisol Levels and Psychological Stress Are Associated With Onset of Secretory Activation of Human Milk Production

BACKGROUND

Several factors can influence the production of mothers' own milk.

PURPOSE

To assess the influence of maternal psychological stress, maternal cortisol levels, and neonatal hair cortisol levels on timing of secretory activation.

METHODS

A prospective study was conducted at 2 public health centers in Andalusia, Spain. Participants were 60 pregnant women and their 60 neonates. Hair cortisol levels and psychological stress (pregnancy-specific stress [Prenatal Distress Questionnaire, PDQ] and perceived stress [Perceived Stress Scale, PSS]) were evaluated during the third trimester and the postpartum period. This study was part of the GESTASTRESS cohort study on the effects of stress during pregnancy.

RESULTS

Higher PDQ and PSS scores (P < .05) in the third trimester were associated with later onset of secretory activation. Higher postpartum maternal hair cortisol levels were associated with a delayed secretory activation of mother's own milk (P < .05).

IMPLICATIONS FOR RESEARCH

Future studies should look at the influence of psychological stress and cortisol levels on hormones involved in mother's own milk production.

IMPLICATIONS FOR PRACTICE

Neonatal nurses and other healthcare providers should be familiar with levels of neonates' exposure to maternal prenatal stress prior to birth.

Minimal breast milk transfer of rituximab, a monoclonal antibody used in neurological conditions

Objective

To determine the transfer of rituximab, an anti-CD20 monoclonal antibody widely used for neurologic conditions, into mature breast milk.

Methods

Breast milk samples were collected from 9 women with MS who received rituximab 500 or 1,000 mg intravenous once or twice while breastfeeding from November 2017 to April 2019. Serial breast milk samples were collected before infusion and at 8 hours, 24 hours, 7 days, and 18–21 days after rituximab infusion in 4 patients. Five additional patients provided 1–2 samples at various times after rituximab infusion.

Results

The median average rituximab concentration in mature breast milk was low at 0.063 μg/mL (range 0.046–0.097) in the 4 patients with serial breast milk collection, with an estimated median absolute infant dose of 0.0094 mg/kg/d and a relative infant dose (RID) of 0.08% (range 0.06%–0.10%). Most patients had a maximum concentration at 1–7 days after infusion. The maximum concentration occurred in a woman with a single breast milk sample and was 0.29 μg/mL at 11 days postinfusion, which corresponds with an estimated RID of 0.33%. Rituximab concentration in milk was virtually undetectable by 90 days postinfusion.

Conclusions

We determined minimal transfer of rituximab into mature breast milk. The RID for rituximab was less than 0.4% and well below theoretically acceptable levels of less than 10%. Low oral bioavailability would probably also limit the absorption of rituximab by the newborn. In women with serious autoimmune neurologic conditions, monoclonal antibody therapy may afford an acceptable benefit to risk ratio, supporting both maternal treatment and breastfeeding.

Lanadelumab for the treatment of hereditary angioedema

Introduction: Hereditary angioedema due to C1 inhibitor deficiency (C1-INH-HAE) is a rare yet still probably underdiagnosed clinical condition. Recurrent episodes of subcutaneous and sub-mucosal swelling may involve the skin, the gastrointestinal tract or even the upper airways, exposing the patients to the risk of death. With the aim of improving patients' quality of life, the therapeutic scenario has expanded over the years.Areas covered: The focus of the present review is lanadelumab, a fully human, κ-light-chain, monoclonal immunoglobulin G1 against plasma kallikrein, currently approved for long-term prophylaxis of C1-INH-HAE attacks in the USA and Canada and designated as an orphan drug by the European Medicines Agency.Expert opinion: Lanadelumab is able to inhibit plasma kallikrein with high selectivity and affinity. The subsequent phases of drug development and the ongoing open-label trial have proven its safety and efficacy. It overcomes some of the limitations of other drugs available for long-term prophylaxis, given the easy route of administration, the simple administration schedule and the possibility to tailor the treatment to each patient. Further studies are needed to test its efficacy also in other types of angioedema for which a central role of plasma kallikrein is envisaged.

Infectious episodes during pregnancy, at particular mucosal sites, increase specific IgA1 or IgA2 subtype levels in human colostrum

Background

Colostrum is the primary source of maternal immunoglobulin A (IgA) for the newborn. IgA participates in protection and regulation mechanisms of the immune response at the neonate’s mucosa. Several studies have evaluated infectious diseases and vaccine protocols effects during pregnancy on maternal milk IgA levels, with the aim to understand lactation protecting effect on newborn. However, most of their results demonstrated that there were no differences in the total IgA levels. In humans, IgA has two subclasses (IgA1 and IgA2), they have an anatomical distribution among mucosal compartments, their levels vary after antigen stimulation and are also seen to describe differential affinities in colostrum. Although there are differences between IgA subclasses in several compartments, these studies have excluded specific colostrum IgA1 and IgA2 determination.

Methods

We analyzed data from 900 women in Mexico City. With Pearson correlation, we compared the number of infectious episodes during their pregnancy that was associated with mucosal compartments (skin, respiratory and gastrointestinal tracts) and colostrum IgA subclasses.

Results

We show a correlation between increased colostrum IgA1 levels and the number of infectious episodes at respiratory tract and the skin. In contrast, infections at the gastrointestinal tract correlated with increased IgA2 amounts.

Conclusions

Infections present during pregnancy at certain mucosal site increase specific IgA subclasses levels in human colostrum. These results will help in understanding infections and immunizations effects on maternal IgA at the mammary gland, and their impact on the development and protection of the newborn.

Electronic supplementary material

The online version of this article (10.1186/s40748-019-0104-x) contains supplementary material, which is available to authorized users.

Innovative Techniques of Processing Human Milk to Preserve Key Components

Human milk not only contains all nutritional elements that an infant requires, but is also the source of components whose regulatory role was confirmed by demonstrating health-related deficiencies in formula-fed children. A human milk diet is especially important for premature babies in the neonatal intensive care unit (NICU). In cases where breastfeeding is not possible and the mother's own milk is insufficient in volume, the most preferred food is pasteurized donor milk. The number of human milk banks has increased recently but their technical infrastructure is continuously developing. Heat treatment at a low temperature and long time, also known as holder pasteurization (62.5 °C, 30 min), is the most widespread method of human milk processing, whose effects on the quality of donor milk is well documented. Holder pasteurization destroys vegetative forms of bacteria and most viruses including human immunodeficiency virus (HIV) herpes and cytomegalovirus (CMV). The macronutrients remain relatively intact but various beneficial components are destroyed completely or compromised. Enzymes and immune cells are the most heat sensitive elements. The bactericidal capacity of heat-pasteurized milk is lower than that of untreated milk. The aim of the study was for a comprehensive comparison of currently tested methods of improving the preservation stage. Innovative techniques of milk processing should minimize the risk of milk-borne infections and preserve the bioactivity of this complex biological fluid better than the holder method. In the present paper, the most promising thermal pasteurization condition (72 °C-75 °C,) and a few non-thermal processes were discussed (high pressure processing, microwave irradiation). This narrative review presents an overview of methods of human milk preservation that have been explored to improve the safety and quality of donor milk.

Effect of HTST and Holder Pasteurization on the Concentration of Immunoglobulins, Growth Factors, and Hormones in Donor Human Milk

Donor human milk (DHM) is submitted to Holder pasteurization (HoP) to ensure its microbiological safety in human milk banks but this treatment affects some of its bioactive compounds. The objective of this work was to compare the effects of HoP and high temperature short time (HTST) treatments on some bioactive compounds found in DHM. A total of 24 DHM batches were processed in a continuous HTST system (70, 72, and 75°C for 5-25 s) and by HoP (62.5°C for 30 min). The concentrations of immunoglobulins (Igs) A, G, and M, transforming growth factor-beta 2 (TGF-β₂), adiponectine, ghrelin, and leptin were measured using a multiplex system, whereas the concentration of epidermal growth factor (EGF) was determined by ELISA. In relation to Igs, IgG showed the highest preservation rates (87-101%) after HTST treatments, followed by IgA (54-88%) and IgM (25-73%). Ig retention after any of the HTST treatments was higher than after HoP (p < 0.001). Treatment times required to reduce the concentration of IgM by 90% (D-value) were 130, 88, and 49 s at 70, 72, and 75°C, while the number of degrees Celsius required to change the D-value by one factor of 10 (z-value) was 11.79°C. None of the heat treatments had a significant effect on the concentrations of TGF-β₂, EGF, adiponectin, and ghrelin. In contrast, leptin was detected only in 4 of the samples submitted to HoP, whereas it was present in all samples after the different HTST treatments, with retention rates ranging between 34 and 68%. Globally, the concentration of IgA, IgG, IgM, and leptin in DHM was significantly higher after HTST pasteurization performed in a continuous system designed to be used in human milk banks than after the HoP procedure that is routinely applied at present.

Cytokines in milk and the role of TGF-beta

Cytokines are required for normal growth and development of the mammary gland and TGF-β prominently represents an established effector of apoptosis, e.g., during involution of the mammary gland. By the control of intracellular signaling pathways, including JAK/STAT, MAPK, PI-3K, and NF-κB, cytokines efficiently regulate cell proliferation and inflammation in the breast. Therefore, cytokines are discussed also in a context of malignant mammary growth. As a group of tissue hormones produced by somatic cells or by cells from the immune system, cytokines are defined by their immunomodulatory potential. Over the past 40 years, multiple cytokines were identified in colostrum and milk. Importantly, cytokines derived from mammary secretions after birth are required for maturation of the immune system in the developing gastrointestinal tract from the suckling. Moreover, recent studies have further assessed the particular interactions between probiotic bacterial strains and cytokines. In light of the increasing prevalence of inflammatory diseases of the gastrointestinal system, the effects of probiotic microorganisms during milk fermentation may have immunotherapeutic potential in the future.