Purification and characterization of an 18-kd allergen of birch (Betula verrucosa) pollen: identification as a cyclophilin.
BACKGROUND
Five birch pollen allergens have been identified so far. In a previous study we detected new birch pollen allergens with an isoelectric point in the range 9.0 to 9.3, present only in extracts prepared at controlled basic pH.


OBJECTIVE
The purpose of the current study was to purify and characterize those allergens.


METHODS
The target allergens were purified by ion exchange and hydrophobic interaction chromatography. Analyses were carried out by SDS-PAGE, isoelectric focusing, immunoblotting, and amino acid sequencing. The in vivo reactivity of the allergens was evaluated by skin testing.


RESULTS
An 18-kd protein, which we named Bet v 7, was purified. This 18-kd protein corresponded to 3 bands on isoelectric-focusing immunoblots that probably represent isoforms. On immunoblots up to 20.8% of birch pollen-allergic patients recognized those allergens. The clinical relevance of Bet v 7 was demonstrated by positive immediate-type skin testing on a patient allergic to birch pollen. Sequencing of an internal peptide yielded an amino acid sequence showing high homology with various plant cyclophilins. The rotamase activity of the protein, inhibited by cyclosporin A, further confirmed that Bet v 7 belongs to the group of cyclophilins.


CONCLUSIONS
We have purified a novel allergen of birch pollen, Bet v 7, belonging to the cyclophilin family. Because cyclophilins are highly conserved proteins over the phylogeny, we may postulate that Bet v 7 is a member of a new family of panallergens.
Cadot
P
P
Laboratory of Experimental Immunology, Faculty of Medicine, Rega Institute for Medical Research, Catholic University of Leuven, Leuven, Belgium.
Diaz
J F
JF
Proost
P
P
Van Damme
J
J
Engelborghs
Y
Y
Stevens
E A
EA
Ceuppens
J L
JL
D000485:Allergens / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification* / Q000378:metabolism; D000595:Amino Acid Sequence; D052179:Antigens, Plant; D016572:Cyclosporine / Q000378:metabolism; D006801:Humans; D006967:Hypersensitivity / Q000097:blood / Q000276:immunology; D015151:Immunoblotting; D007073:Immunoglobulin E / Q000097:blood; D020104:Immunophilins / Q000276:immunology / Q000302:isolation & purification* / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D019696:Peptidylprolyl Isomerase / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification*; D011058:Pollen / Q000737:chemistry* / Q000276:immunology; D012882:Skin Tests; D014197:Trees / Q000737:chemistry* / Q000276:immunology
D000485:Allergens; D052179:Antigens, Plant; C405762:Bet v 7 protein, Betula verrucosa; D010940:Plant Proteins; D007073:Immunoglobulin E; D016572:Cyclosporine; D020104:Immunophilins; D019696:Peptidylprolyl Isomerase