In vitro studies reveal immunomodulatory effects of probiotic bacteria that are strain-dependent. Differential immunomodulatory in vitro capacities can not be extrapolated directly to in vivo efficacy. Thus, in vitro screening should be followed by comparative analysis of the selected immunomodulatory probiotic strains in an in vivo setting. Birch pollen allergy is one of the most common forms of respiratory allergy in European countries, and recognized by a Th2-skewed immune system. Five Lactobacillus strains will be evaluated for their immunomodulatory properties in birch pollen sensitive subjects outside the hay fever season. A double-blind placebo-controlled parallel study will be performed in which subjects with a proven birch pollen allergy will consume one of 5 different probiotic yoghurts containing 4 L. plantarum strains and 1 L. casei strain or a placebo yoghurt. Blood samples are collected at the start and after 4 weeks. Immune parameters are determined in serum and peripheral blood mononuclear cell cultures (hPBMC) derived from these subjects.

Inclusion Criteria:

• birch pollen sensitive subjects
• Positive RAST or intracutane skintest
• age 18-50
• signed informed consent form

Exclusion Criteria:

• use of probiotics
• known allergy for pets (home setting)
• use of medication influencing the immune system
• use of antibiotics
• lactose intolerance
• pregnancy
• infection