Mutational analysis of the IgE epitopes in the latex allergen Hev b 5

BACKGROUND

Hev b 5 is a major latex allergen and potential candidate for an immunotherapy reagent.

OBJECTIVE

The purpose of this study was to produce a hypoallergenic form of Hev b 5.

METHODS

We used SPOTs analysis with alanine substitution to identify amino acids (AAs) critical for IgE binding and used site-directed mutagenesis to produce recombinant proteins with altered IgE-binding activity.

RESULTS

Eleven epitopes were identified (5.1-5.11) in Hev b 5. Individual patients demonstrated variable epitope recognition, with the most intense reactivity to epitopes 5.4 and 5.7. IgE inhibition assays with synthetic peptides indicated that mutating a single epitope would not reduce IgE binding, but rather a combination of epitopes was required. After alanine substitutions to identify the important AAs, site-directed mutagenesis was used to replace the crucial AAs with alanine. Twenty clones with different combinations of altered epitopes were evaluated by means of IgE inhibition assays. Clones with mutations in single epitopes failed to reduce IgE binding, but changes to 8 epitopes (14 AAs) resulted in a 4500-fold reduction in IgE binding. Epitopes 5.7 and 5.9 were found to be cross-reactive, making Hev b 5 a multivalent allergen.

CONCLUSIONS

We produced a recombinant Hev b 5 protein with significantly reduced IgE-binding activity. Changing a minimum of 3 immunodominant epitopes was required to cause a 100-fold reduction in IgE binding. Changes in 8 epitopes, particularly the cross-reactive epitopes 5.7 and 5.9, were needed to maximize the reduction in IgE binding. Mutants with reduced IgE-binding activity may prove to be valuable reagents for immunotherapy.

Human IgE-binding epitopes of the latex allergen Hev b 5

BACKGROUND

Hev b 5 is an acidic protein (isoelectric point, 3.5) rich in glutamic acid with 9 repeated amino acid (AA) sequences of XEEX or XEEEX. Although its function in Hevea brasiliensis is unknown, Hev b 5 has been identified as a major latex allergen. Immunoblot inhibition studies suggest Hev b 5 exists as multiple isoforms or contains a common epitope found in several other proteins.

OBJECTIVE

The purpose of this study was to further characterize Hev b 5 and to identify linear IgE-binding epitopes.

METHODS

Octapeptides spanning the entire Hev b 5 protein were synthesized on a derivatized cellulose membrane. The membrane was reacted with sera pooled from health care workers allergic to latex or rabbits immunized with latex proteins. B-cell epitopes were identified by subsequent incubations with the appropriate secondary antibodies and detected by using chemifluorescence.

RESULTS

Sera from patients allergic to latex recognized 6 IgE-binding regions located throughout the molecule. Two epitopes (2 and 4) had the common AA sequence of KTEEP. Epitopes 3 and 5 had a similar AA sequence of EEXXA, where X was P, T, or K. Epitopes 1 and 6 appeared to be unrelated to the other epitopes. Database analysis could not identify other proteins with similar sequences. Neither of the XEEEX sequences bound IgE. Control sera failed to react to any peptides.

CONCLUSIONS

Hev b 5 exists as multiple isoforms, but only small amounts are present in the nonammoniated latex preparations, such as those used for diagnostic tests, and this may help to explain the relatively poor sensitivity of some in vitro tests.

Cloning and characterization of a latex allergen (Hev b 7): homology to patatin, a plant PLA2

We previously identified a 46-kD protein allergen in latex as having amino acid sequence homology to the patatin gene family. The objective of this study was to characterize this protein by molecular techniques. RNA was isolated from the latex or leaf material from Hevea brasiliensis and from potato tubers. Specific polymerase chain reaction (PCR) primers were designed from the amino acid sequence and reverse transcriptase (RT)-PCR amplified a specific product from latex RNA that was subsequently cloned and sequenced. This product was 1493 bp in length with an 1167 bp open reading frame. The deduced amino acid sequence encodes for a 389 aa protein, pI 4.82 with 43% homology to tobacco patatin. Northern analysis of potato, Hevea leaf, and latex RNA demonstrated the message to be most abundant in latex, weakly present in Hevea leaf, but no hybridization occurred with potato RNA. Patatin has lipid acyl-transferase and PLA2-like activity, suggesting it plays a role as a defence-related protein. Other defence-related proteins in latex such as hevein, glucanase, and hevamine are also allergens. Increased production of defence-related proteins as a result of increased tapping of the rubber trees to meet the demand for latex may explain the increased allergenicity of latex.

Interactions between angiotensin II and adenosine 3':5'-cyclic monophosphate in the regulation of amino acid transport by vascular smooth muscle cells

The regulation of amino acid transport by angiotensin II (AII) and cyclic AMP (cAMP) was assessed in cultured vascular smooth muscle cells, using a nonmetabolizable amino acid, alpha-[3H]aminoisobutyric acid (AIB). An exposure time in excess of 2 h was required for AII to elicit a stimulatory response, the magnitude of which increased in a time-dependent manner for 12 h. AII-induced transport was blocked by [1-sarcosine, 8-isoleucine]AII, a competitive inhibitor of AII binding. The effect of AII was not abolished by downregulation protein kinase C with phorbol 12,13-dibutyrate or by use of a protein kinase C inhibitor, suggesting that transport in response to AII can be mediated by a protein kinase C independent pathway. In contrast, the elimination of calcium from the incubation medium reduced AII-stimulated AIB uptake. The calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide partially inhibited AIB uptake in response to AII, suggesting that calmodulin may be involved in the modulation of AII-stimulated amino acid transport. AIB transport was also increased by elevating intracellular cAMP levels via beta-adrenergic receptor stimulation, the use of a cAMP analog (N6-monobutyryl cAMP), or a phosphodiesterase inhibitor (3-isobutyl-1-methylxanthine) or by direct stimulation of adenylate cyclase with forskolin. cAMP-induced AIB transport was evident within 10 min and peaked within 1 h. At 1 h AII enhanced cAMP-stimulated AIB transport. A possible mechanism for this effect is suggested by the observation that AII potentiated cAMP production in response to isoproterenol and 3-isobutyl-1-methylxanthine.