Maternal antibodies are certainly transferred from mother to child, both in utero through placental transfer as well as through breast milk. Whether protective antibodies specific for certain allergens are transferred from mother to child in general and from allergic mother to child in particular is still not clear. Best one can do is estimate relative risk based on peer-reviewed human epidemiological or interventional studies, many of which come with their fair share of shortcomings which this answer also details.
Transfer of Maternal antibodies
Human antibody classes are IgD, IgM, IgG (IgG1, IgG2, IgG3, IgG4), IgA and IgE. Of these, only IgG is known to be transferred across the placenta (see figure below from 1).
Since fetal B cells are still immature at birth, IgG found in fetal blood circulation is presumed to originate in the mother and transported intact into fetal circulation (2, 3, 4, 5). This requires a special pathway (see figure below from 2).
Can Maternal IgG transferred in utero help protect baby from allergies?
- One study (6) gave mothers a specific immunotherapy during pregnancy and then analyzed their children’s tendency for allergic sensitization. Results suggested blocking antibodies induced by the immunotherapy were transferred across the placenta and may have been responsible for reduced allergic sensitization effect in children.
- Another study (7) found that high cord blood concentrations of IgG specific for inhaled allergens correlated with reduced atopy in children.
- A third study found maternal antibodies could transiently, not permanently, reduce children’s allergic immune responses (8). Why transient? Because these effects were strong at birth but had waned by 2 years of age.
- Of the IgG sub-classes, IgG4 may have a protective affect against allergies in children (8, 9, 10, 11).
Caveats to these studies: Individual reports with small numbers of subjects, 18 (6), 96 (7), and 49 (8), respectively. Principle can only be generalized if confirmed by multiple studies across multiple ethnicities and broad range of allergens. It may even be that such a protective effect isn’t generalizable across a range of allergies, for example, different protective mechanisms may be crucial for food versus inhaled versus skin allergens.
What about IgE, the main antibody implicated in allergies?
IgE is one of the dominant pathologic antibody responses associated with cat allergy symptoms. Maternal IgE is not known to be transferred to the infant, either in utero or through breast milk, so child likely won’t acquire pathogenic anti-cat IgE from cat-allergic mother.
- However, maternal IgE to the cat allergen Fel d 1 is linked to increased childhood wheezing risk for the child (12). Fel d 1 is the major cat allergen associated with cat allergies.
- In addition, maternal history of asthma plus cat allergen exposure also increases risk of childhood wheezing (13).
Is IgA, transferred through breast milk post-birth, protective against allergies?
Breast milk is abundant in SIgA (secretory IgA). Though IgA constitutes a relatively small proportion of circulating antibodies, its enormous abundance in mucosal tissues renders it the predominant antibody in humans (14). It’s present in two forms. One is serum IgA, mostly monomeric and largely produced by B cells in the bone marrow. The other is Secretory IgA (SIgA), produced locally by mucosal tissue-resident B cells. SIgA is dimeric. The secretory component attached to it also makes it more resistant to cleavage by proteolytic enzymes. In contrast to IgE, SIgA is potentially protective antibody in asthma and allergies (15). Allergen-specific SIgA can bind to the allergen and flush it out of the body, preventing it from being internalized and then driving allergic immune responses in the child. So this is in general. Is there specific data relating to cat allergies?
- One study (16) of 17 allergic and 36 non-allergic mothers found similar levels of anti-cat allergen SIgA in both groups. The good news for an allergic mother in this data is it suggests that at least her allergy might not result in lower anti-cat allergen SIgA being transferred to her baby. However, the study has problems which limit its implications. One, small number of subjects. Two, mothers’ allergies weren’t clearly outlined.
- However, a meta-analysis of 56 studies published between 1996 and 2001 found that >50% of them reported breast milk protected against atopic dermatitis and asthma, especially in children with a parental history of atopy (17).
So, in sum, the answer’s a mixed bag. On the one hand, it’s unlikely that allergen-specific IgE might be transmitted from mother to child, either in utero or through breast milk, i.e., less likelihood of transfer of allergic immune responses from mother to child. However, the mother’s anti-allergen IgE levels appear to correlate with increased allergy risk for child down the road. OTOH, allergen-protective IgG and SIgA antibodies can be transferred from mother to child, and they may protect the new-born transiently against particular allergies. So a child may be temporarily protected post-birth but an individual’s lifelong allergy risk is multi-factorial. Many other factors influence a child’s lifelong risk for allergy. Some of the more important ones, or at least better studied ones include maternal smoking and diet during pregnancy, mode of delivery*, and presence and dose of allergen in the early years. However, unlike dogs, where meta-analysis of epidemiological studies suggests their presence during a child’s first years is largely protective against allergies to dog, the data’s not so clear for cats.
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