D1.66 - Allergy profiling in selective goat and sheep milk allergy

Background / Objectives

In Spain, cow’s milk protein allergy (CMPA) is the second most common food allergy in childhood, with an estimated prevalence of approximately 8%. Allergy to goat’s and sheep’s milk is usually attributed to cross-reactivity due to the high structural homology of caseins among mammalian species. However, selective allergy to goat’s and sheep’s milk with preserved clinical tolerance to cow’s milk is an infrequent and poorly described condition. The aim of this report is to present two cases of selective allergy supported by a detailed immunological study.

Case Report

We report two pediatric patients, aged 6 and 10 years, who developed several episodes of anaphylaxis (Müller grade II) after ingestion of white chocolate and assorted cheeses, respectively. The cheese products contained cow’s, goat’s and sheep’s milk, while the white chocolate included milk powder without specification of its origin. Both patients had previously tolerated cow’s milk and its derivatives without adverse reactions.

Allergy evaluation showed positive skin prick tests to goat’s and sheep’s milk, and negative results for cow’s milk in both patients.

In patient 1, prick-prick testing with white chocolate was negative. Specific IgE assessed by Allergy Explorer Macroarray Diagnostic was negative for cow’s milk, with sensitization to sheep’s milk (3.80 kU/L) and goat’s milk (4.66 kU/L).

In patient 2, skin prick tests were positive for cow’s milk, casein, α-lactalbumin and β-lactoglobulin, as well as prick-prick positivity to goat’s milk, sheep’s milk and different cheeses. Specific IgE levels determined by ImmunoCAP were low for cow’s milk (0.98 kU/L) and and casein (2.64 Ku/l) in comparison to goat’s and sheep’s milk (>100 kU/L).

Immunoblotting analysis revealed IgE recognition of several protein bands, predominantly within the molecular weight range of caseins in both patients, with no recognition of the corresponding cow’s milk bands. Additional bands between 50 and 75 kDa were also observed. Inhibition assays with goat’s and sheep’s milk demonstrated nearly complete inhibition of IgE binding for both kind of milks.

Conclusion

Until now, the reported selective allergy to to goat’s and sheep’s milk allergy was explained by cross-reactivity among specific epitopes of the caseins of both species. In these cases, in addition to recognition of caseins, sensitization to higher molecular weight bands not described in other series were found. They could correspond to serum albumins or neo-epitopes generated during food processing. The inhibition tests assessed the high homology among these proteins of both species.