This study aims to determine if there is a link between cow's milk allergy in infants and regulatory T cells dysfunction that should be transient in infant acquiring oral tolerance after 12 month avoiding food and persistent in others.

Cow's milk allergy is evaluated by basophils activation test, T cells activation test, specific humoral response (IgA, IgE, IgG) in allergic infants before and after 12 month avoiding food, before and after low dose milk exposure, before and after oral challenge.

Number and function of regulatory T cells and microflora composition are measured at the same time.

Allergic infants are compared to age matched control group.

Inclusion Criteria:

male or female, age before 6 month, cow's milk allergy with positive prick or patch test for cow's milk

Control group: male or female, age before 6 month or within 12 and 18 month, eating cow's milk every day

Exclusion Criteria:

immunodeficiency syndrome, lactose intolerance Control group: other food allergy, atopic dermatitis.