Bovine milk-derived allergen specific IgG antibodies

The results of this project will thus help to explain the mechanisms behind the link between raw milk consumption and asthma, and may lead to novel approaches in the prevention of asthma via nutritional supplementation with functionally intact bovine IgG.

Background

Over the last 20 years evidence is accumulating that growing up on a farm is associated with a decreased prevalence of asthma and rhinitis.
It has been demonstrated in several large epidemiological studies that this effect is linked independently to on the one hand the consumption of unprocessed raw cow’s milk and on the other hand to microbial exposure via farm animals and stables.

Several studies have also shown that the effect of farm milk consumption is only seen when the farm milk is not heated before consumption, strongly suggesting that it is linked to the presence of non-denatured milk proteins. The effects of milk proteins on human immune function have been studied by several groups including ours, and have shown that bovine milk proteins can have an effect on human immune function. Milk contains immune regulatory cytokines such as immunoglobulins, especially IgG, lactoferrin, TGF-, and many other proteins with an immunological function.

Bovine IgG (bIgG) is of special interest in relation to the reduced risk of asthma, because it can bind to respiratory viruses such as RSV and influenza, that are associated with an enhanced risk to develop asthma, as well as to other human pathogens like E coli, Salmonella, Streptococcus pneumoniae. bIgG has downstream effector function in the human system as well, as it binds to FcRII, has been shown to induce phagocytosis of bacteria and viruses, to enhance RSV-specific T cell activation through the formation of RSV-bIgG immune complexes, and even to completely inhibit infection of human cells with RSV in vitro. In addition to these pathogens, bovine milk IgG may also bind to allergens, which has only been addressed in a single study to date.

Project description

In asthma, immune complexes of IgE with allergens have been shown to play an important role in facilitating Th2 responses in the presence of low allergen doses. Binding of IgE-allergen complexes to CD23 or FcRI results in receptor-mediated allergen uptake and antigen presentation to allergen-specific T cells. Upon allergen immunotherapy, this effect is inhibited by the action of blocking IgG antibodies, thus strongly increasing the allergen dose needed to activate allergen-specific T cells that perpetuate the allergic immune response, but are also of key importance in the late phase asthmatic response.

CD23 may have an additional function in allergen-specific responses in the respiratory tract via the of IgE and allergen-IgE immune complexes over the respiratory. Inhibition of CD23-mediated IgE transcytosis over respiratory epithelium has been shown to inhibit allergic airway inflammation. Blocking this CD23-mediated transport might be an additional effect of allergen-specific blocking IgG (and IgA) antibodies.
These blocking allergen-specific antibodies can also inhibit the degranulation of basophils and mast cells, both by physically hindering allergen-IgE interactions as well as IgG-allergen binding to the inhibitory CD32b receptor on these effector cells. A strong indication for the clinical relevance of blocking IgG antibodies in treatment of allergic patients has come from treatment of cat and birch pollen-allergic patients with recombinant IgG antibodies specific for cat and birch pollen. In these studies Regeneron has developed sets of potent allergen-blocking monoclonal IgG antibodies against the major cat allergens Fel d 1 and Bet v 1 and observed that already at day 8 after administration the blocking IgG antibodies had the same effect to that reported with years of conventional allergen immunotherapy.

More recently, the presence of allergen-IgG complexes in breast milk has been shown to prevent the development of allergy in early life in two murine model systems. Although the presence of allergen-IgG immune complexes has only been shown directly in animal model systems, the presence of allergen-specific IgG as well as the presence and the allergens themselves has been confirmed in human breast milk. These data indicate that during early life the oral presence of allergen-IgG immune complexes may drive the formation of allergen-specific immune tolerance, and might be instrumental in preventing respiratory allergies. In early life respiratory allergens that enter the body through the nose or mouth are swallowed, and thus come into contact with milk proteins in tonsils and even adenoids, indicating the possibility that bIgG-allergen immune complexes might at least in part explain the epidemiological findings of the association of raw milk consumption with a lower asthma incidence.

The role of these allergen-specific IgG, IgA and IgE antibodies in sensitization and in the elicitation phase of respiratory allergies has recently been reviewed.

It is interesting that a single paper already in the early 1990s has indicated that bIgG may also be able to bind to allergens. This finding is especially relevant in the light of the more recent epidemiological findings of a link between raw milk consumption and asthma. In preliminary experiments we have been able to show that bIgG can bind to house dust mite allergens. In the future there might be a role of functionally active bIgG in passive allergen immunization for immediate symptom relief in asthma, such as in the studies with allergen-specific IgG mAbs, or in enhancing tolerization to allergens in early life nutrition.
We hypothesized therefore, that dietary intake of bovine IgG has the ability to modulate sensitization and allergic responses to respiratory allergens (see figure 1). To this aim we characterized the ability of bIgG to bind to a large panel of well characterized asthma-related respiratory allergens, quantified their levels, evaluated their capacity to inhibit the formation and receptor binding of allergen-IgE complexes, and further evaluated the potential effects of this binding on IgE-dependent responses.

Results

In colostrum, raw milk products and commercially available pasteurized cow’s milk bovine IgGs were present in high amounts against the mites D.farinae, D. pteronyssinus, the fungi A.alternata, A. fumigatus, C. herbarum and P.notatum, grasses sweet vernal, orchard, timothy and cultivated rye, hazel tree pollen and ragweed. Some moderate IgG binding was found for alder, birch and oak tree pollen and mugwort and English plantain. No IgG binding was detected to cat, dog and horse allergens. The IgG levels in raw milk differed between different farms, but was comparable to that found in pasteurized cow’s milk.

Commercially available sterilized (Ultra high temperature treated) cow’s milk was completely missing any IgGs for the aeroallergens tested.
Bovine IgG could inhibit the binding of serum IgE to the allergens to some extent. Further, binding of housedust mite-IgE and grass pollen-IgE immune complexes was shown usingHDM- and grass- allergic donors. Although values were generally slightly lower, preincubation with bovine IgG had no significant blocking effect on binding of IgE immune complexes to CD23-expressing B cells. Likewise, the bovine IgG could also not inhibit the HDM-dependent release of basophils. From an allergic donor.

Conclusion: Cow’s milk contains significant levels of IgGs against the most common aeroallergens, which are lost after sterilization. Even though these do not compete significantly with allergen-specific IgE, they are known to bind to human FcRII and may have immune-modulatory effects that are yet to be explored. This might explain the decreased allergy prevalence association with raw milk consumption. Further studies will examine the functional properties of these allergen-specific IgGs in cow’s milk.