Properties of caseins and allergenicity

CANDREVA ANGELA; DOCENA GUILLERMO H.; PETRUCCELLI SILVANA

CASEINS: PROPERTIES, FUNCTIONS AND HEALTH IMPLICATIONS

Nova Science Publishers

Año: 2016; p. 77 - 102

Cow milk allergy (CMA) is an aberrant reaction to the in principle harmless cow milk proteins (CMP). CMA is the most frequent cause of food allergy in childhood and several reasons are responsible of highest prevalence, among then early introduction of CMP in the infant diet, nature of the cow milk (CM) allergens and genetic background. Most of CMA individuals are sensitized to several CMPs: caseins (CAS), -lactalbumin (ALA), -lactoglobulin (BLG), bovine serum albumin (BSA), lactoferrin and immunoglobulins (Ig), but only CAS, ALA and BLG are considered major allergens. There is still controversy about the role of individual CM allergens in primary sensitization and pathogenesis, but CAS are the most frequently IgE recognized CMP. CAS, known as Bos d 8 allergen, is heterogeneous fraction formed by S1- (Bos d 9), S2- (Bos d 10), - (Bos d 11) and - (Bos d 12) casein. Foreignness to the affected host is one of the features expected for allergen, at this respect S1, - and -CAS have sequence identity degrees with human homologs of 33, 54, 55%, respectively. In contrast, ALA (Bos d 4), BSA (Bos d 6) and lactoferrin (Bos d lactoferrin) sequence identity is over 70%, and proteins with more than 62% of identity are rarely allergic. BLG (Bos d 5) and S2-CAS are absent in human breast milk therefore are stranger. There is also a causal relationship between resistance to proteolysis and allergenicity. Although isolated caseins are easy degraded, in mammalian milk they are associated in micelles that are resistant to proteolysis. In correlation with this, desphosphorylation desestabilice micelle structure reducing CAS allergenicity. In addition CAS have P,Q-rich sequences that promote promiscuous interactions typical of heat shock proteins. These types of motifs are able to stimulate both humoral and cellular response, stressing role of CAS in pathogenesis. Avoidance is the recommended treatment for allergy and replacement with milk of other ruminants is not advised, since cross-reactivity is detected among caseins of different species. Studies with animal models demonstrate that caseins are able to break the mucose intestinal epithelial barrier, what also contribute to sensitization. In conclusion CAS have several structural and molecular properties that inforce its central role in CMA.