Side-chain-specific lymphocyte responses in workers with occupational allergy induced by penicillins

Immunologic Basis for Adverse Reactions to Radiographic Contrast Media

The lymphocyte transformation test (LTT) was used to elucidate whether certain side effects induced by radiographic contrast media have an immunologic etiology. Groups studied were: 8 patients who had previously experienced adverse reactions in association with urography, 6 patients who underwent urography without notable side reactions, 17 occupationally exposed nurses, and 9 unexposed controls. The lymphocytes from 2 hypersensitive patients and from 11 nurses exhibited a positive proliferative response to amidotrizoate. Five nurses who had shown a positive response, had a previous history of hypersensitivity reactions when handling contrast media, whereas the remaining 6 were free of symptoms. Amidotrizoate-specific memory cells were absent in patients who underwent urography without signs of hypersensitivity and in 7/9 of unexposed control subjects. Lymphocytes from patients sensitive to amidotrizoate cross-reacted to structurally related ionic contrast media while non-ionic contrast agents did not induce proliferation of the lymphocytes. Thus, ionic radiographic contrast agents have antigenic properties in man. Irradiated mixtures of radiographic contrast media and serum proteins were, in general, not effective in inducing an LTT response.

Penicillin dust exposure and penicillin resistance among pharmaceutical workers in Tehran, Iran

BACKGROUND

Antimicrobial resistance (AMR) adversely impacts the prevention and treatment of a wide range of infections and is considered as a serious threat to global public health. Occupational-related AMR is a neglected area of research.

OBJECTIVE

To assess exposure to penicillin dust, penicillin active materials, and to report the frequency of penicillin resistance among pharmaceutical workers in Tehran, Iran.

METHODS

A quasi-experimental study was conducted among workers on a penicillin production line in a pharmaceutical company (n = 60) and workers in a food producing company (n = 60). Data were collected via survey, air sampling, and throat swab.

RESULTS

The mean overall concentrations of penicillin dust and penicillin active material were 6.6 and 4.3 mg/m³, respectively, in the pharmaceutical industry. Streptococcus pneumoniae (S. pneumoniae) was detected in 45% (27) individuals in the exposed group, 92.6% of which showed penicillin resistance. Resistance was significantly higher among workers in penicillin production line (p = 0.014).

CONCLUSIONS

High level of AMR among workers in penicillin production line is a health risk for the workers as well as society as a whole through the spread of drug resistant micro-organisms.

Nonimmediate reactions to betalactams

PURPOSE OF REVIEW

Nonimmediate reactions to beta-lactams include several clinical entities, from maculopapular rash to severe reactions such as Steven-Johnson syndrome. Toxic epidermal necrolysis and organ-specific reactions may also occur.

RECENT FINDINGS

Progress has been made in understanding the role of the immunological system in nonimmediate reactions to beta-lactams. Different T-cell subsets recognize beta-lactams after haptenation of serum or cell proteins in the context of major histocompatibility complex. Studies using T-cell lines and clones have shown that a heterogeneous response is generated, with the expression of different cytokine profiles. Betalactams also act on dendritic cells, inducing changes that enable them to interact with naïve lymphocytes, becoming memory T cells. Tissue-activated CD4 and CD8 cells express perforin and other cytotoxic mediators that elicit the lesions. Studies on the clinical course of these entities indicate that cells migrate, establishing a recirculation with homing to the skin and back to the circulation. These cells thus participate not only in skin lesions but probably also in the repair process.

SUMMARY

Understanding the immunological mechanisms involved in nonimmediate reactions to beta-lactams has improved over the last few years, with better definition of the different T-cell subpopulations involved. Experimental studies and monitoring of the response support the implication of different cell subsets.

Characterization of primary recall in vitro lymphocyte responses to bacampicillin in allergic subjects

BACKGROUND

Antigen-specific cell lines or clones are often used as models of drug-specific allergy. However, cloning procedures are time consuming, and the repeated antigen stimulation cycles as well as the addition of various growth enhancers may affect the in vivo relevance of these systems.

OBJECTIVE

Using bacampicillin-allergic subjects, we wanted to investigate the applicability of primary recall in vitro lymphocyte responses to characterize type I and type IV allergy. The sensitivity and specificity of LTT (Lymphocyte transformation test), when used as an in vitro diagnostic tool, were also assessed.

METHODS

A total of 39 patients with symptoms of type I (rhinitis) or type IV (allergic contact dermatitis, ACD) allergy following occupational exposure to bacampicillin, were included. Ten individuals without penicillin allergy or occupational exposure to bacampicillin served as controls. All subjects were LTT tested. Four patients with rhinitis and two patients with ACD were available for studying the immunophenotype and the TCR-Vbeta repertoire of bacampicillin induced lymphoblasts as well as the cytokine profiles and expression of the activation markers CD23 and CD134 in primary PBMC cultures.

RESULTS

LTT was positive in 87% and at least one of the skin tests was positive in 85% of the patients with allergic symptoms. 69% of the patients with type I allergies were patch test-positive. Results from LTT and skin test correlated in 87% of the cases. The combined sensitivity of LTT and skin tests was 92%. The specificity of LTT was 90% in healthy controls. Bacampicillin induced lymphoblasts were mainly CD4 + in both ACD and rhinitis patients. The TCR-Vbeta profiles of the predominant CD4 + lymphoblasts were heterogeneous with individual skewing towards Vbeta2, Vbeta3, Vbeta5.1 and/or Vbeta14. An increased expression of IFNgamma was detected in bacampicillin treated PBMC cultures from the ACD but not from rhinitis patients. IL-5 was detected in bacampicillin exposed PBMC cultures from all patients but not from healthy controls. This Th2 environment could also be verified by CD23 and CD134 expression.

CONCLUSION

LTT and skin tests are equally sensitive in identifying bacampicillin allergic subjects. When the two tests are combined, the sensitivity increases. The patch test is useful not only for detection of type IV but also for the identification of type I allergies. When using primary PBMC cultures, IFNgamma is the most suitable cytokine to discriminate between type I and type IV allergy. IL-5 can possibly be used as a general marker for bacampicillin induced allergy. Thus, primary cell cultures may be considered as an alternative to T-cell lines or clones for the study of drug induced allergy.

Occupational airway sensitizers: an overview on the respective literature

BACKGROUND

Worldwide, there is rigorous scientific activity concerning the further development of work safety regulations involving airway-sensitizing substances. Technical directives on hazardous substances are enforced in several countries and are being continuously updated. The European Union has established a code for several occupational substances, now labeled R 42 ("may cause sensitization by inhalation").

METHODS

We present an overview of the literature dealing with allergic occupational asthma. The literature was selected according to criteria of study design and diagnostic test methods. Approximately 300 publications were reviewed including both epidemiological studies and individual case reports.

RESULTS

Airway sensitizers are systematically arranged and separately listed according to chemicals and their origin from animals, plants, and microorganisms. The clinical data as well as threshold limit values (TLV) and R 42 labeling of 250 airway-sensitizing substances are presented.

CONCLUSIONS

The most common sensitizing substances causing occupational asthma were dust of cereal flours, enzymes, natural rubber latex, laboratory animals as well as low molecular substances such as isocyanates and acid anhydrides.

In vitro lymphoproliferative assays with HgCl2 cannot identify patients with systemic symptoms attributed to dental amalgam

Dental amalgam is suspected, by some exposed individuals, to cause various systemic psychological, sensory, and neurological symptoms. Since not all amalgam-bearers experience such reactions, an individual characteristic--for example, a susceptible immune system--might explain these conditions. In vitro lymphocyte proliferation is a valuable tool in the diagnosis of allergy. With HgCl2 as the antigen, however, the test is hampered, because Hg2+ can cause unspecific lymphocyte proliferation, optimal at 1.4 to 9.5 micrograms HgCl2/mL. Recently, the use of suboptimal HgCl2 concentrations (< or = 0.5 microgram/mL) has been suggested to circumvent these problems. The main aim of this study was to investigate whether patients with systemic symptoms alleged to result from the presence of dental amalgam differ from healthy controls, with reference to in vitro lymphoproliferative responses to HgCl2 < or = 0.5 microgram/mL. Three different test protocols--lymphocyte transformation test (LTT) in micro- and macro-cultures, and the memory lymphocyte immunostimulation assay (MELISA)--were used. Other immune parameters--such as a standard patch test for dental materials, the number of T- and B-lymphocytes, monocytes, granulocytes, and NK cells in peripheral blood, allergic symptoms, and predisposition--were also investigated. Twenty-three amalgam patients, 30 healthy blood donors with amalgam, ten healthy subjects without amalgam, and nine patients with oral lichen planus (OLP) adjacent to dental amalgam and a positive patch test to Hg0 were tested. None of the investigated immune parameters revealed any significant differences between amalgam patients and controls. The sensitivity of in vitro lymphocyte proliferation ranged from 33 to 67%, with the OLP patients as a positive control group, and the specificity from 0 to 70% for healthy controls with a negative patch test to Hg0. Thus, despite the use of HgCl2 < or = 0.5 microgram/mL, a high frequency of positive results was obtained among healthy subjects with or without dental amalgam. Consequently, in vitro lymphocyte proliferation with HgCl2 cannot be used as an objective marker for mercury allergy in dental amalgam-bearers.

In vitro lymphocyte proliferation in the diagnosis of allergy to phenoxymethylpenicillin

BACKGROUND

The aim of this study was to investigate in vitro lymphocyte proliferation in the diagnosis of allergy to phenoxymethylpenicillin (PcV), comparing chemically reactive PcV, added to cell cultures in unconjugated form, to a PcV-PLL (poly-L-lysine) conjugate as antigens. Side-chain specificity of lymphoproliferative responses was investigated with reactive benzylpenicillin (PcG) and bacampicillin.

METHODS

Seventeen patients with a history of hypersensitivity reactions in connection with PcV treatment were studied by means of the lymphocyte transformation test (LTT), the radioallergosorbent test (RAST), skin tests (prick and intracutaneous), and oral challenge with PcV. LTT was also performed in 20 control subjects exposed to PcV therapeutically, and in eight subjects with occupational exposure to this penicillin.

RESULTS

Nine patients had a positive in vivo test to PcV (five by oral challenge, three by intracutaneous test, and one by both tests), and six were challenge-negative. When reactive PcV was used as antigen in LTT, positive LTT responses were observed in five of the nine patients with a positive in vivo test, and two of them were also side-chain specific. Positive LTT responses with reactive PcV also correlated with a positive RAST in five of seven subjects. None of the six patients with a negative challenge test, and only one of the 28 controls showed a positive LTT result with reactive PcV. Thus, the specificity of LTT with reactive PcV was 96%. In contrast, when PLL-conjugated PcV served as antigen, four challenge-negative subjects and 11 controls were LTT-positive.

CONCLUSIONS

The results of this study indicate that LTT with chemically reactive PcV could be useful as an in vitro complement in the diagnosis of PcV allergy and as a tool to reveal the side-chain specificity of peripheral blood lymphocytes. A positive LTT to PLL-conjugated PcV may be an indicator of immunization, but not necessarily allergy, to the penicilloyl structure.

Allergic nephropathy associated with norfloxacin and ciprofloxacin therapy. Report of two cases and review of the literature

Allergic nephropathy associated with quinolone antibiotics has been reported in an increasing number of cases. The mechanism might be a hypersensitivity reaction. Norfloxacin has been incriminated previously as a cause once only, with acute interstitial nephritis (AIN) as the histopathological finding. Ciprofloxacin-associated nephropathy has been reported in 28 cases, with AIN as the main histopathological finding. This report describes a second case of AIN associated with norfloxacin treatment and another ciprofloxacin-associated renal interstitial drug adverse reaction. Clinicians should be aware of quinolone-associated AIN, which is a rare but potentially dangerous renal complication.

Nonimmediate reactions to betalactams: prevalence and role of the different penicillins

In patients treated with penicillins, adverse cutaneous reactions can occur within minutes or may take several days to develop. IgE antibody-mediated reactions are well documented, but other mechanisms may also be involved. In particular, nonimmediate reactions have not been studied extensively, and the purpose of the present work was to establish the incidence of such reactions among a large group of patients and to study the penicillins involved. A total of 380 subjects with a history of a cutaneous reaction following administration of a penicillin antibiotic was included in the study. Skin tests and specific IgE measurements (RAST) were carried out using various penicillins and penicillin-related reagents, and patients were also challenged with various penicillins. In some patients with delayed skin test responses, skin biopsies were carried out. The tests confirmed that 74 subjects (19.4% of total investigated) had suffered a cutaneous reaction to a penicillin derivative, and 29 of these subjects (7.6% of total or 39% of confirmed) showed evidence of having suffered a nonimmediate reaction. The latter group were identified by giving a positive delayed direct challenge, and in 65% of the cases a delayed skin test response was detected. In most cases, these responses were to amino penicillins. Skin biopsies showed a lymphomonocytic cell infiltrate. Nonimmediate reactions to penicillins are a reproducible phenomenon, suggesting that a specific mechanism is responsible. By direct challenge, 93% of responders were positive to amino penicillins (10.3% ampicillin, 82.7% amoxicillin), indicating a major role for these penicillins in nonimmediate reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of adverse cutaneous reactions to aminopenicillins with emphasis on those manifested by maculopapular rashes

We assessed 195 subjects with histories of adverse reactions to aminopenicillins, using 1) skin tests with penicilloyl polylysine (PPL), minor determinant mixture (MDM), benzylpenicillin (PG), amoxicillin, and ampicillin (read after 20 min and 48 h); 2) patch tests with PG, amoxicillin, and ampicillin; and 3) RAST for penicilloyls G and V. Oral challenges with ampicillin, amoxicillin, and penicillin V were administered to 34/60 patients reporting maculopapular reactions. Immediate hypersensitivity (IH), in most cases for both penicillin and aminopenicillins, was diagnosed (based on skin tests, RAST, or both) in 35 subjects who had suffered anaphylactic shock, or urticaria, angioedema, or both urticaria and angioedema. Thirty-three of the 60 subjects reporting maculopapular reactions presented delayed intradermal and patch-test positivity, indicating delayed hypersensitivity (DH), for ampicillin and amoxicillin, and three were also positive for PG. Diagnoses were confirmed with oral challenges in 18/33. The remaining 27/60 were negative in all allergologic tests, with oral-challenge confirmation in 16. Our findings highlight the importance of the amino group in DH to aminopenicillins. Moreover, the mean time interval between the last reaction and our tests was significantly (P < 0.01) longer in DH subjects (54.96 months) than in those with IH (18.62 months), suggesting that the time of testing is less important in cases of DH.

Sulfonamide-reactive lymphocytes detected at very low frequency in the peripheral blood of patients with drug-induced eruptions

BACKGROUND

The role of T lymphocytes in mediating drug eruptions is uncertain.

METHODS

Twenty-four patients with eruptions induced by sulfonamide-related drugs were studied to detect lymphocyte reactivity to drugs. Both the lymphocyte transformation test and limiting dilution analysis were used as assays for drug-reactive lymphocytes. Peripheral blood lymphocytes were expanded in interleukin-2 and tested for reactivity to sulfamethoxazole and furosemide.

RESULTS

The lymphocyte transformation test results to sulfamethoxazole, sulfisoxazole, and furosemide were found to be generally unreliable with a high rate of false-negative and false-positive results. However, as determined by limiting dilution analysis, sulfamethoxazole-reactive lymphocytes were detected in the peripheral blood of one patient at a frequency of 1/172,000. This is within the lower range of frequencies of urushiol-reactive T cells in the peripheral blood of patients with allergic contact dermatitis to urushiol (poison ivy). Two sulfonamide-reactive lymphocyte lines were cultured from two patients. Both lines proliferated in response to sulfamethoxazole but not in response to furosemide, suggesting that furosemide does not cross-react with the sulfonamides.

CONCLUSIONS

Lymphocytes reactive to sulfamethoxazole were detected at low frequencies in the peripheral blood of three patients with drug eruptions secondary to administration of sulfamethoxazole.

Predominance of epidermal CD8+ T lymphocytes in bullous cutaneous reactions caused by beta-lactam antibiotics

The phenotype and functional characteristics of skin-infiltrating lymphocytes in beta-lactam antibiotic-induced vesiculobullous exanthemas were studied in vivo and in vitro. Immunohistochemical analysis demonstrated that CD8+ T lymphocytes were the predominant epidermal T-cell subset in these reactions. Epidermal T lymphocytes were isolated and expanded for in vitro studies. Fluorescence-activated cell sorter analysis showed the majority of epidermal T cells to be CD3+, T-cell receptor alpha/beta+, CD4-, CD8+, and HLA-DR+, which correlated with the predominance of epidermal CD8+ T lymphocytes found in situ. Three CD8+ epidermal T-cell clones derived from cutaneous lesions proliferated in response to penicillin-pulsed autologous antigen-presenting cells but not allogeneic antigen-presenting cells, indicating that those clones were antigen and major histocompatibility complex specific. All T-cell clones produced significant amounts of interleukin-2, interferon-gamma, and granulocyte-macrophage colony-stimulating factor. Additionally, the T-cell clones displayed cytotoxicity against epidermal cells in lectin-mediated cytotoxicity and against B-cell lines in T-cell receptor-triggered cytotoxicity. These data demonstrate the presence of epidermal drug-specific CD8+ T cells in bullous drug reactions. Because these CD8+ T cells have a cytotoxic potential, they may contribute to the necrosis of keratinocytes associated with drug-induced blister formation.

Selective generation of CD8+ T-cell clones from the peripheral blood of patients with cutaneous reactions to beta-lactam antibiotics

The presence, phenotype, and functional characteristics of peripheral blood penicillin-specific T lymphocytes in individuals with cutaneous allergic reactions to penicillin were investigated using in vitro long-term culture techniques. Peripheral blood mononuclear cells from two penicillin-allergic patients were stimulated in vitro with penicillin, and T-cell blasts were clonally expanded by limiting dilution. Seven T-cell clones were derived, all of which were CD3+ CD4- CD8+ HLA-DR+, and produced IL-2 and IFN-gamma upon stimulation. T-cell proliferation required the presence of antigen and autologous, but not allogeneic, antigen-presenting cells. In addition to the parent compound, the T-cell clones also developed a proliferative response to penicilloyl, the major metabolite of penicillin. The cloned T-cell lines were found to exhibit marked suppressor activity for Con A mitogenesis. The observed suppressor activity required cell-to-cell contact, as supernatants from these T-cell clones had no comparable inhibitory effect. These findings indicate that there is a predominance of penicillin-specific CD8+ T cells in the peripheral blood of individuals sensitized to beta-lactam antibiotics.

Lymphocyte Transformation Tests in Workers with Occupational Exposure to Spiramycin

Pharmaceutical industry employees are exposed to drugs which can stimulate allergic reactions. Other authors have found that, in workers of pharmaceutical companies exposed to spiramycin, spiramycin-induced asthma can be diagnosed only on the basis of spiramycin inhalation tests, because IgE specific antibodies, as well as skin and patch tests, are often negative.

Since lymphocytes from humans sensitised to various agents undergo morphological transformation on exposure to sensitising antigen in culture, we used a lymphocyte transformation test (LTT) following in vitro exposure to spiramycin of cells collected from healthy workers occupationally exposed or not exposed to this antibiotic.

LTT was measured by [3H]-thymidine uptake into DNA of lymphocytes cultured for three days in medium containing 0-500μg/ml spiramycin. The number of lymphoblasts was also counted on cell smears. Lymphocytes from spiramycin-exposed subjects, incubated with spiramycin, demonstrated a statistically significant increase of [3H]-thymidine incorporation; the presence of lymphoblasts in the cultures was only slightly increased.

Although other experiments with lymphocytes obtained from patients with spiramycin-induced asthma need to be performed, this pilot study suggests that LTT may be able to be used to detect early immune response changes caused by chemical agents in occupationally exposed workers.

Delayed allergic reactions to beta-lactams. Four cases with intolerance to amoxicillin or ampicillin and good tolerance to penicillin G and V

We present four cases of delayed allergic skin reactions to amoxicillin or ampicillin with good tolerance to benzyl penicillin and phenoxymethyl penicillin. The clinical symptoms reported by the patients, the intradermal skin tests and the controlled challenge results suggested that the mechanism was cellular mediated. In two patients these findings were supported by histopathological studies. Although delayed-type hypersensitivity reactions to beta-lactams with positive skin test seem rare, they can occur to penicillins in allergic patients. The production of these reactions by amoxicillin or ampicillin with good tolerance to benzyl penicillin and phenoxymethyl penicillin emphasizes the role of the side chain in inducing allergic reactions to beta-lactams.

Contribution of biological markers to occupational health

Occupational diseases are now being assessed at the cellular and molecular levels; this presents new opportunities for prevention and control [Calleman et al., 1978; Ong et al., 1987; Stejskal et al., 1989; Welch and Cullen, 1988; Garry et al., 1989]. The key to these opportunities is the ability to detect biological markers that reflect exposure, response, and susceptibility. Biological markers are not new, however. Biological markers such as blood lead, urinary phenol levels in benzene exposure, and liver function assays have long been used in occupational and public health research and practice. What distinguishes the current generation of markers from previous markers is a greater degree of analytical sensitivity and the ability to describe events that occur earlier in the progression between exposure and clinical disease. There are now new domains of response that were not known to exist 20 years ago. Accompanying this sensitivity is the increased requirement to consider the numerous factors that can influence the appearance of biological markers. It has been observed that all workers with similar exposures do not develop disease or markers indicative of exposure or disease. Various acquired and hereditary host factors are responsible for this variation in responses. The role of assessing the nature and degree of variation between individuals is of paramount importance. Finally, the use of biological markers in occupational health research and practice also brings new ethical and legal considerations into high profile. This paper presents my personal opinions on how biological markers can contribute to occupational health efforts and the new requirements that they bring to the field. As with any technological change, the more we can anticipate the impact, the better our ability to adjust.

Lymphocyte transformation test for diagnosis of isothiazolinone allergy in man

The lymphocyte transformation test (LTT) has been used for evaluation of in vitro lymphocyte responses in 18 patients with dermatitis and positive patch tests to 200 ppm of a combination of 5-chloro-2-methylisothiazolinone and 28methylisothiazolinone (MCI) in nine patients with dermatitis unrelated to MCI and in seven subjects without skin diseases. Two workers sensitized by occupational exposure to a formulation containing 1,2-benzisothiazolin-3-one (BIT) were also studied. Lymphocytes from nine patch-test-positive patients proliferated vigorously to MCI in vitro. Lymphocytes from the remaining nine patients were not stimulated. Lymphocytes from two BIT-sensitized workers responded to BIT in vitro. The lymphocyte proliferation to isothiazolinones indicates the presence of memory cells in the patients' blood and confirms immunologic reaction to the inducing agent. To establish clinical relevance of LTT results, 12 MCI patch-test-positive patients underwent "use test" with lotion containing 15 ppm MCI. Four of five LTT-positive patients were use-test-positive, whereas seven of seven LTT-negative patients were use-test-negative. LTT-positive and lotion-positive patients responded to 100 ppm or lower concentrations of MCI on patch testing, whereas seven of eight LTT-negative and lotion-negative patients responded to 200 ppm only. In the case of MCI, proliferation was due to the chlorinated component, indicating that this part contains an allergenic epitope. Finally, MCI-specific lymphocyte proliferation was observed only in patients with MCI-positive skin test, but not in nine patients with dermatitis induced by other agents, or in seven subjects without skin diseases. Thus, the lymphocyte transformation test is able to distinguish between irritant and allergic skin responses. It may also be valuable in establishing the clinically relevant patch-test concentration of allergens with irritative properties.

The specificity of the lymphocyte transformation test in a patient with hypersensitivity reactions to pyrazolone compounds. A 10-week follow-up study before and after rechallenge

To evaluate the specificity of the lymphocyte transformation test (LTT) in the diagnosis of drug allergy we studied over 71 days an atopic woman with a past history of frequent adverse reactions to pyrazolone drugs. Rechallenge with the incriminated substances aminophenazone (aminopyrine) and propyphenazone was carried out on Days 11 and 31 respectively. An immediate type of hypersensitivity reaction was seen after 100 mg aminophenazone, while 100 mg of propyphanozone led to a serum sickness-like syndrome. We found two specifically sensitized lymphocyte populations using either the pure substance or sera containing metabolite in cell cultures. Stimulatory responses with indices ranging between 3 and 6 were seen 3-4 days after exposure, and the tests remained positive in both instances for 3-4 weeks. Specific sensitization was proven by positive skin tests and by a small but distinct lymphocyte proliferative response before challenge. Several lymphocyte function tests were performed over a period of 53 days and revealed a large fall in pokeweed mitogen-induced immunoglobulin synthesis and an increase in suppressor cell activity after rechallenge with aminophenazone. We conclude that the proliferative response observed in the presence of the offending drug is due to the activation of T memory cells and therefore highly suggestive of a true allergic reaction.