The recombinant major allergen of Parietaria judaica and its hypoallergenic variant: in vivo evaluation in a murine model of allergic sensitization.
BACKGROUND
Par j 1 represents the major allergenic component of Parietaria judaica pollen. Its three-dimensional structure is stabilized by four disulphide bridges. A family of three-dimensional mutants of the recombinant Par j 1 (rPar j 1) allergen, showing reduced allergenicity and retained T cell recognition has been recently developed by site-directed mutagenesis.


OBJECTIVE
To develop and characterize a murine model of IgE sensitization to rPar j 1. To evaluate similarities between the murine model and the human IgE response. To investigate in this model the recognition of a hypoallergenic mutant of Par j 1, and to study the immune responses elicited in mice by the mutant itself.


METHODS
BALB/c mice were sensitized by two intraperitoneal immunizations with rPar j 1 in alum on days 0 and 21. Allergen-specific serum IgE and IgG responses were studied by direct ELISA and immunoblotting, ELISA inhibition and competitive ELISA. Cell proliferation was evaluated in splenocyte cultures.


RESULTS
Sensitization with rPar j 1 induced high levels of IgE and IgG1 vs. low levels of IgG2a. Mouse antibodies specific to rPar j 1 were able to compete with human IgE for recognition of rPar j 1. IgE from mice immunized with rPar j 1 showed a significantly reduced binding activity towards the hypoallergenic variant rPjC, which lacks three disulphide bridges. On the contrary, rPjC was recognized by IgG1 and IgG2a antibodies as well as rPar j 1. The proliferative response to rPjC by splenocytes from mice immunized with rPar j 1 was comparable to that stimulated by rPar j 1. Immunization with rPjC induced low levels of IgE antibodies to the rPjC itself, while IgG and proliferative responses were similar to those induced by rPar j 1.


CONCLUSIONS
Conformational variants of allergens, displaying reduced allergenicity accompanied by retained IgG and T cell recognition, offer a safe, specific and flexible approach to immunotherapy of type I allergy. Our mouse model of IgE sensitization to a recombinant allergen, mimicking the human response to its native counterpart, could provide valuable information for pre-clinical testing of such hypoallergenic molecules.
Orlandi
A
A
Laboratory of Immunology, Istituto Superiore di Sanità, Rome, Italy.
Grasso
F
F
Corinti
S
S
Marinaro
M
M
Bonura
A
A
Boirivant
M
M
Colombo
P
P
Di Felice
G
G
D000485:Allergens / Q000276:immunology*; D000818:Animals; D000906:Antibodies / Q000276:immunology; D000937:Antigen-Antibody Reactions; D002455:Cell Division; D003888:Desensitization, Immunologic; D005260:Female; D006967:Hypersensitivity / Q000276:immunology / Q000517:prevention & control; D007073:Immunoglobulin E / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D023421:Models, Animal; D032403:Parietaria / Q000276:immunology*; D010940:Plant Proteins / Q000276:immunology*; D011058:Pollen; D011994:Recombinant Proteins / Q000276:immunology; D013154:Spleen / Q000166:cytology
D000485:Allergens; D000906:Antibodies; D007074:Immunoglobulin G; C083860:Par j I protein, Parietaria judaica; D010940:Plant Proteins; D011994:Recombinant Proteins; D007073:Immunoglobulin E