Mucosal tolerance is an immunological phenomenon specific to mucosal surfaces as found in the lungs and gastro-intestinal tract. It results in the suppression of immune responses to inhaled or ingested antigens and prevents the body from unwan-ted and unnecessary immuno-logical responses to harmless molecules, such as grass-pollen or food constituents. This imposes the difficult task for the immune system of keeping a balance between reacting and non-reacting, and disturbances of this balance result in allergies and possibly autoimmunity, as well as opportunistic infections and even an escape from tumor surveillance. Understanding the mechanisms that underlie mucosal tolerance is, therefore, important from different viewpoints. Maintenance or (re)induction of mu-cosal tolerance to, e.g., food proteins, airborne allergens or autoantigens is desirable to prevent or cure allergies and autoimmune diseases. However, induction of mucosal tolerance is an unwanted phenomenon in mucosal vaccination and in the case of mucosal tumors.
Nasal provocation tests with histamine and methacholine were carried out in 25 healthy men on an effort to assess the dynamic changes of albumin, total IgA, secretory IgA and lactoferrin concentrations in the nasal secretion. The trials were performed with 0.5, 1, and 4 mg of histamine and 8, 16, 32 mg of methacholine. Each dose of histamine or methacholine was sprayed into a nose every second day, and with two days interval between two provocating agents. The nasal secretions were collected after saline spraying only forming baseline group and after 3, 10 and 15 minutes of the challenge agent administration. The baseline levels presented the following values: for albumin 257? 230 mug/ml, secretory IgA 608 ? 379 mug/ml, total IgA 1025 ? 423 mug/ml, and lactoferrin 213 ? 156 mug/ml. The increase of albumin level after nasal provocation, particularly significant after histamine administration (to 3713 ? 2311 mug/ml), indicates the incessant protein plasma leaking from the blood circulation to the nasal secretion. After administration of both provocating agents there was the significant gradual decrease of secretory IgA level, even below the baseline value. After the 2nd and the 3rd doses of methacholine and histamine spraying the concentration of secretory IgA decreased 2-3 times and was found to be 200-300 mug/ml, respectively. Also, lactoferrin concentration values decreased gradually after the 2nd and 3rd doses of methacholine and histamine to level close the baseline value. These observations suggest time and dose dependent, a non-specific dysfunction of local immunity response after nasal provocations.
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