Infant milk formulas differ regarding their allergenic activity and induction of T-cell and cytokine responses.

BACKGROUND: Several hydrolyzed cow's milk (CM) formulas are available for avoidance of allergic reactions in CM-allergic children and for prevention of allergy development in high-risk infants. Our aim was to compare CM formulas regarding the presence of immunoreactive CM components, IgE reactivity, allergenic activity, ability to induce T-cell proliferation, and cytokine secretion. METHODS: A blinded analysis of eight CM formulas, one nonhydrolyzed, two partially hydrolyzed (PH), four extensively hydrolyzed (EH), and one amino acid formula, using biochemical techniques and specific antibody probes was conducted. IgE reactivity and allergenic activity of the formulas were tested with sera from CM-allergic patients (n = 26) in RAST-based assays and with rat basophils transfected with the human FcεRI, respectively. The induction of T-cell proliferation and the secretion of cytokines in Peripheral blood mononuclear cell (PBMC) culture from CM allergic patients and nonallergic individuals were assessed. RESULTS: Immune-reactive α-lactalbumin and ß-lactoglobulin were found in the two PH formulas and casein components in one of the EH formulas. One PH formula and the EH formula containing casein components showed remaining IgE reactivity, whereas the other hydrolyzed formulas lacked IgE reactivity. Only two EH formulas and the amino acid formula did not induce T-cell proliferation and proinflammatory cytokine release. The remaining formulas varied regarding the induction of Th2, Th1, and proinflammatory cytokines. CONCLUSION: Our results show that certain CM formulas without allergenic and low proinflammatory properties can be identified and they may also explain different outcomes obtained in clinical studies using CM formulas.

Patients suffering from non-IgE-mediated cow's milk protein intolerance cannot be diagnosed based on IgG subclass or IgA responses to milk allergens.

BACKGROUND: Cow's milk is one of the most common causes of food allergy. In two-thirds of patients, adverse symptoms following milk ingestion are caused by IgE-mediated allergic reactions, whereas for one-third, the mechanisms are unknown. Aim of this study was to investigate whether patients suffering from non-IgE-mediated cow's milk protein intolerance can be distinguished from persons without cow's milk protein intolerance based on serological measurement of IgG and IgA specific for purified cow's milk antigens. METHODS: We determined IgG(1-4) subclass and IgA antibody levels to purified recombinant αS1-casein, αS2-casein, ß-casein, κ-casein, α-lactalbumin, and ß-lactoglobulin in four patient groups by ELISA: Patients with IgE-mediated cow's milk allergy (CMA, n=25), patients with non-IgE-mediated cow's milk protein intolerance (CMPI, n=19), patients with gastrointestinal symptoms not associated with cow's milk ingestion (GI, n=15) and control persons without gastrointestinal problems (C, n=26). Cow's milk-specific IgE levels were determined by ImmunoCAP. RESULTS: Only CMA patients had IgE antibodies to cow's milk. Cow's milk allergic patients mounted the highest IgG(1) and IgG(4) antibody levels to αS1-casein, αS2-casein, ß-casein, κ-casein, and α-lactalbumin. No elevated levels of IgG(4) , IgA, and complement-binding IgG subclasses (IgG(1) , IgG(2) , IgG(3) ) to purified cow's milk allergens were found within the CMPI patients compared to persons without cow's milk protein intolerance (GI and C groups). CONCLUSION: Cow's milk protein intolerant patients cannot be distinguished from persons without cow's milk protein intolerance on the basis of IgG subclass or IgA reactivity to cow's milk allergens.

Microarray and allergenic activity assessment of milk allergens.

BACKGROUND: Cow's milk is one of the most common causes of food allergy affecting approximately 2.5% of infants in the first years of their life. However, only limited information regarding the allergenic activity of individual cow's milk allergens is available. OBJECTIVE: To analyse the frequency of IgE reactivity and to determine the allergenic activity of individual cow's milk allergens. METHODS: A nitrocellulose-based microarray, based on purified natural and recombinant cow's milk allergens was used to determine IgE reactivity profiles using sera from 78 cow's milk-sensitized individuals of varying ages. The allergenic activity of the individual allergens was tested using patients' sera for loading rat basophil leukaemia cells (RBL) expressing the α-chain of the human receptor FcεRI. RESULTS: Using the microarray and the RBL assay, cow's milk allergens were assessed for frequency of IgE recognition and allergenic activity. Moreover, the RBL assay allowed distinguishing individuals without or with mild clinical reactions from those with severe systemic or gastrointestinal symptoms as well as persons who grew out cow's milk allergy from those who did not. CONCLUSIONS: Component-resolved testing using milk allergen microarrays and RBL assays seems to provide useful additional diagnostic information and may represent a basis for future forms of prophylactic and therapeutic strategies for cow's milk allergy.

Sensitization to human milk.

BACKGROUND: Allergy to milk is one of the earliest manifestations of IgE-mediated allergies and affects about 2.5% of newborn children. Several reports indicate that milk-allergic patients may be sensitized also to human milk proteins. OBJECTIVE: To analyse the specificity and possible biological relevance of IgE reactivity to human milk antigens in milk-allergic patients. METHODS: The specificity of IgE reactivity to cow's milk and human milk antigens was analysed with sera from milk-allergic children and adults by IgE immunoblotting. IgE cross-reactivity between milk antigens was studied by immunoblot inhibition experiments. That IgE reactivity to human milk antigens is not due to alloreactivity or due to the transmission of foreign antigens into mother's milk was demonstrated through the analysis of milk samples from genetically unrelated mothers before and after intake of dietary milk products. The biological relevance of IgE reactivity to human milk was confirmed by skin testing. Results IgE antibodies to human milk were found in more than 80% of the tested milk-allergic patients. Cross-reactive IgE-reactive human antigens such as alpha-lactalbumin and non-cross-reactive human milk antigens were identified. Immediate-type skin reactions could be elicited with human milk samples in patients with IgE reactivity to human milk. CONCLUSION: IgE reactivity to human milk in milk-allergic patients can be due to cross- sensitization and genuine sensitization to human milk and may cause allergic symptoms. IgE-mediated sensitization to human milk is common in milk-allergic patients and may require diagnostic testing and monitoring.

Molecular aspects of the ribosomal peptidyl transferase.

The proteins in a living cell are synthesized on a large bipartite ribonucleoprotein complex termed the ribosome. The peptidyl transferase, which polymerizes amino acids to yield peptides, is localized on the large subunit. Biochemical investigations over the past 35 years have led to the hypothesis that rRNA has a major role in all ribosomal functions. The recent high resolution X-ray structures of the ribosomal subunits clearly demonstrated that peptidyl transfer is an RNA-mediated process. As all ribosomal activities are dependent on bivalent metal ions, as is the case for most ribozymes, we investigated metal-ion-binding sites in rRNA by metal-ion-cleavage reactions. Some cleavage sites are near active sites and are evolutionarily highly conserved. The structure of the active site is flexible and undergoes changes during translocation and activation of the ribosome. Using modified P-site substrates, we showed that the 2'-OH group of the terminal adenosine is important for peptidyl transfer. These substrates were also used to investigate the metal ion dependency of the peptidyl transferase reaction.

A conformational change in the ribosomal peptidyl transferase center upon active/inactive transition.

The ribosome is a dynamic particle that undergoes many structural changes during translation. We show through chemical probing with dimethyl sulfate (DMS) that conformational changes occur at several nucleotides in the peptidyl transferase center upon alterations in pH, temperature, and monovalent ion concentration, consistent with observations made by Elson and coworkers over 30 years ago. Moreover, we have found that the pH-dependent DMS reactivity of A2451 in the center of the 23S rRNA peptidyl transferase region, ascribed to a perturbed pKa of this base, occurs only in inactive 50S and 70S ribosomes. The degree of DMS reactivity of this base in the inactive ribosomes depends on both the identity and amount of monovalent ion present. Furthermore, G2447, a residue proposed to be critical for the hypothesized pKa perturbation, is not essential for the conditional DMS reactivity at A2451. Given that the pH-dependent change in DMS reactivity at A2451 occurs only in inactive ribosomes, and that this DMS reactivity can increase with increasing salt (independently of pH), we conclude that this observation cannot be used as supporting evidence for a recently proposed model of acid/base catalyzed ribosomal transpeptidation.