Background: Bovine casein leads to an expansion of lymphocytes expressing the cutaneous lymphocyte antigen and to specific lymphocyte proliferation in a subgroup of patients with milk-responsive atopic dermatitis (AD). The casein fraction is composed of different proteins with defined and completely different sequences.
Objective: To define the stimulatory capacity of the major casein protein (alpha, beta and kappa) in lymphocyte proliferation assays with cells from milk-allergic and non-allergic individuals.
Methods: Proliferative responses of peripheral blood mononuclear cells to lipopolysaccharide-depleted casein subfractions were measured by thymidine incorporation. Lymphocytes from milk-responsive patients with AD were compared with cells from non-responsive patients with AD and to non-atopic individuals. Atopic individuals with immediate symptoms following consumption of cow's milk were included as positive controls. Casein-specific T-cell clones (TCC) from four patients with milk-responsive AD were restimulated with unfractionated casein and kappa-casein.
Results: Higher proliferative responses to unfractionated casein and alpha-, beta- and kappa-casein were observed in milk-responsive patients compared with non-responders. Unfractionated casein and kappa-casein discriminated best between the milk-responsive patients with AD and non-responders. Twenty-five of 31 TCG from patients with milk-responsive AD reacted to the mixed casein preparation and kappa-casein.
Conclusion: A pronounced kappa-casein-specific T-cell-mediated immune response is found in the blood of many patients with a history of milk-related exacerbation of AD.