Increase, Allergic Respiratory Hypersensitivity Response

The development of an allergic hypersensitivity reaction in the respiratory tract is a two-step process, first requiring induction of the immune response (Boverhof et al, 2008). Subsequent single or multiple exposures to the same substance result in elicitation of an allergic hypersensitivity reaction, characterized by breathlessness and wheezing, airflow obstruction, bronchoconstriction, and tightness of the chest (Lauenstein et al, 2014). Reactions can be acutely life threatening or lead to chronic occupational asthma (Boverhof et al, 2008).

Clinical signs described above can be objectively assessed in humans to confirm diagnosis of respiratory hypersensitivity. Airflow obstruction and bronchoconstriction are measured using serial measures of airflow (usually FEV1) about 12 hours after exposure to test for immediate or delayed bronchoconstriction (Beckett, 2008). However, to differentiate between irritant and allergic asthma, additional testing to confirm immune involvement must also be conducted.

Allergen-specific IgE detection and measurement techniques include skin tests (intradermal and subcutaneous skin prick testing) and blood testing using immune assays such as ELISAs and commercially available tests such as ImmunoCAP™. For example, Bernstein et al. investigated the ability of TMA skin testing to identify sensitized workers and found that skin prick testing was positive in 8 of 11 workers with serum-specific IgE and intradermal testing in a further two (Bernstein et al., 2011). It is important to note, however, that there are technical challenges associated with detection and measurement of specific IgE and IgG to chemical respiratory allergens, including production of the correct protein conjugate and timing of measurement (Kimber et al., 2014, Quirce, 2014). Immune assays such as ELISA or ImmunoCAP are also used to investigate allergen-specific antibody isotype profiles (Movérare et al., 2017). Investigations into direct and indirect class switching involve transcriptomic analyses of IgE heavy chain transcripts and are challenging due to the scarcity of IgE-switched B cells in human blood (Davies et al., 2013).

In cases where specific IgE cannot be identified, the Basophil Activation Test (BAT) can identify allergic response in patients within a year of the last allergen exposure. Basophils degranulate in response to IgE cross-links bound to the high-affinity IgE receptor, much like mast cells. In fresh blood samples (less than 24 hours old) this can be measured by the translocation of CD63 to the membrane using flow cytometry. A review of the use of BAT in diagnosing occupational asthma shows that BAT is a functional readout that works for a variety of allergens, including dust, latex, and small molecules such as ammonium persulfate, chlorhexidine, and beta-lactam antibiotics. However, 10 - 20% of people are estimated to be BAT non-responders in which this response is not detected (Vera-Berrios et al., 2019).

In vivo, alterations in breathing parameters such as respiratory rate, minute volume, tidal volume, peak expiratory flow, inspiratory and expiratory times and a flow-derived estimation of airflow restriction (enhanced pause, Penh) have been used for quantitative assessment of allergen induced airway hyperreactivity (Boverhof et al. 2008).

In rats, respiratory exposure to diisocyanites leads to immediate and delayed airway response. Elicitation is confirmed measuring PMN in bronchoalveolar lavage fluid (BAL) one day after inhalation challenge and exhaled NO (Pauluhn 2014).

The domain of applicability for respiratory sensitisation is primarily limited to humans. Guinea pigs, and to a lesser degree rats, are the only rodent species that exhibit respiratory hypersensitivity, but in guinea pigs, IgG1 is the driver antibody (Boverhof et al 2008). In mice, vascular hypersensitivity is observed rather than respiratory response (Boverhof et al 2008). Therefore investigations in mice are limited to the study of earlier key events, or elicitation of vascular hypersensitivity.

This adverse outcome is of high regulatory interest and relevance, though no test guideline is available. Regulatory agencies and industrial producers are interested in preventing the first step--induction of immune response. Importantly, induction of respiratory sensitisation can be obtained via skin exposure, which is consequential for potential exposure restrictions.

Beckett, W.S., 2005. Revised protocol: criteria for designating substances as occupational asthmagens on the AOEC List of Exposure Codes.

Boverhof DR, Billington R, Bhaskar Gollapudi B, Hotchkiss JA, Krieger SM, Poole A, Wiescinski CM, and Woolhiser MR. 2008. Respiratory sensitization and allergy: Current research approaches and needs. Tox Appl Pharm 226:1-13.

Dearman RJ, Betts CJ, Humphreys N, Flanagan BF, Gilmour NJ, Basketter DA, Kimber I. 2003. Chemical allergy: considerations for the practical application of cytokine profiling. Toxicol. Sci. 71, 137–145.

Lauenstein L, Switalla S, Prenzler F, Seehase S, Pfennig O, Förster C, Fieguth H, Braun A and Sewald K. 2014. Assessment of immunotoxicity induced by chemicals in human precision-cut lung slices (PCLS). Tox in Vitro 28:588–599.

OECD (2010) Test No. 429: Skin Sensitisation: Local Lymph Node Assay, OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing. doi: 10.1787/9789264071100-en.

Pauluhn J. 2014. Development of a respiratory sensitization/elicitation protocol of toluene diisocyanate (TDI) in Brown Norway rats to derive an elicitation-based occupational exposure level. Toxicology 319: 10–22.

BERNSTEIN, J. A., GHOSH, D., SUBLETT, W. J., WELLS, H. & LEVIN, L. 2011. Is trimellitic anhydride skin testing a sufficient screening tool for selectively identifying TMA-exposed workers with TMA-specific serum IgE antibodies? J Occup Environ Med, 53, 1122-7.

DAVIES, J. M., PLATTS-MILLS, T. A. & AALBERSE, R. C. 2013. The enigma of IgE+ B-cell memory in human subjects. J Allergy Clin Immunol, 131, 972-6.

KIMBER, I., DEARMAN, R. J. & BASKETTER, D. A. 2014. Diisocyanates, occupational asthma and IgE antibody: implications for hazard characterization. J Appl Toxicol, 34, 1073-7.

MOVÉRARE, R., BLUME, K., LIND, P., CREVEL, R., MARKNELL DEWITT, Å. & COCHRANE, S. 2017. Human Allergen-Specific IgG Subclass Antibodies Measured Using ImmunoCAP Technology. Int Arch Allergy Immunol, 172, 1-10.

QUIRCE, S. 2014. IgE antibodies in occupational asthma: are they causative or an associated phenomenon? Curr Opin Allergy Clin Immunol, 14, 100-5.

VERA-BERRIOS, R. N., FEARY, J. & CULLINAN, P. 2019. Basophil activation testing in occupational respiratory allergy to low molecular weight compounds. Curr Opin Allergy Clin Immunol, 19, 92-97.