Incidence of IgG short-term sensitizing antibodies in an allergic population*

Harold S. Nelson, M.D., Colonel, Medical Corps, and Leslie B. Branch, M.D., Lieutenant Colonel, Medical Corps Denver, Colo.

Heat-stable, immunoglobulin G, short-term sensitizing antibodies (IgG S-T S) were sought in serum ffom 149 allergic patients who had strongly positive immediate skin tests to inhalant allergens. The sera were tested by passive cutaneous anaphylaxis (PCA) in monkeys. No IgG S-T S antibodies were demonstrated in I69 tests with a variety of allergens. Antibody with the characteristics of IgE was demon&rated in 47% of monkey PCA tests and, in an additional 34% of sera, IgE antibody to the same allergen was demonstrated by radioallergosorbent testing (RAST).

Homocytotropic antibodies bind to the basophils and mast cells of the species in which they are pro- duced, sensitizing these cells to release mediators on exposure to specific antigens. In a number of experi- mental animals two major classes of homocytotropic antibodies have been described which differ markedly in their properties (Table I).

In man, the major homocytotropic, or skin- sensitizing, antibody has been identified as IgE.2 However, there have been a number of reports of the occurrence of skin-sensitizing antibodies in man which differed in major respects from IgE. Some of these skin-sensitizing antibodies have been of the IgG class, and have had many of the characteristics of the “IgG type” antibody described in experimental ani- mals. The evidence for the existence of an IgG skin- sensitizing antibody in man includes: (1) occurrence of an immediate wheal-and-flare skin reaction follow- ing intracutaneous injection of anti-IgG antibody similar to that which occurs with injection of anti- IgE3, and (2) release of histamine from human

From the Allergy/Immunology Service, Fitzsimons Army Medical Center.

Received for publication May 24, 1977. Accepted for publication Aug. 5, 1977. Reprint requests to: Harold S. Nelson, M.D., Colonel, MC, Chief,

Allergy/Immunology Service, Fitzsimons Army Medical Cen- ter, Denver, Colo. 80240.

*The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflect- ing the views of the Department of the Army or the Department of Defense. The protocol under which this study was conducted was approved by the Clinical Research and Human Use Commit- tee of Fitzsimons Army Medical Center and the Office of the Surgeon General, United States Army.

basophils4+’ and both humanlO* l1 and monkey12, l3 lung tissue on exposure to anti-IgG. In each study, the amount of anti-IgG required to elicit a response indi- cated a degree of sensitivity several hundred fold less than to anti-IgE. Also suggesting an IgG homocyto- tropic antibody in man is a report than a human IgG4 paraprotein blocked IgE sensitization of baboon tis- sue. This paraprotein bound to the primate tissue for less than 24 hr.14 Finally, convincing evidence of an IgG homocytotropic antibody in man has been presented by Parish,‘, l1 employing passive cutaneous anaphylaxis (PCA) in monkeys. Based on maximum sensitization of skin sites at 2% hr, persistence of sensitization for less than 24 hr, and resistance to heating to 56“ C, Parish termed this skin-sensitizing antibody the “IgG short-term sensitizing antibody” (IgG S-T S). Further studies by Bryant, Bums, and Lazarus,15, l6 also employing PCA in monkeys, sug- gested that the IgG S-T S antibody might mediate the allergic reaction to house dust mite in 20% to 30% of patients with allergic asthma.

The present study was designed to determine the incidence of IgG S-T S antibodies in a large number of individuals with immediate wheal-and-flare skin test reactions to common inhalant allergens who were undergoing evaluation in an allergy clinic.

MATERIALS AND METHODS Sera from allergic patients

The serum specimens studied were selected from among those drawn from 706 consecutive patients over 8 yr of age who underwent allergy skin testing in our clinic and upon which IgE levels had been determined by the Phadebas technique (Pharmacia Diagnostics, Piscataway , N. J .).

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IgG short-term sensitizing antibodies 267

FIG. 1. The 6 longitudinal rows were sensitized, from left to right, with: Heated serum, 4 hr, unheated serum, 4 hr, unheated serum, 24 hr, normal serum, 2 hr, unheated serum, 2 hr, and heated serum, 2 hr. Evans blue dye followed by cat dander was given intravenously. The seventh serum reacted somewhat at 2 and 4 hr; the tenth serum reacted slightly at 4 hr; otherwise all reactions were in the sites sensitized 24 hr prior to challenge.

Specimens had been stored at -70” C. The majority of samples were duplicates that had not been thawed prior to their use in this study. The selected sera were from those patients who had had at least one 4+ (wheal with psuedopods and surrounding erythema) to 1: 20 w/v (pol- len) or I : 10 w/v (dust and mold) concentrations of allergen extract during routine skin testing.r7 A total of 169 PCA tests were performed with 149 different serum specimens, representing 61% of the 241 patients who had had 4-t prick tests. The clinical diagnoses in these 149 patients were: allergic rhinitis, 95; allergic asthma, 20; both allergic rhinitis and asthma, 25; and miscellaneous conditions, 9.

Passive cutaneous anaphylaxis

Four adult male pigtailed macaque monkeys (Mucaca nemestrina) were used as recipients in PCA testing. Un- der anesthesia with ketamine (1 .O mg/kg) the monkeys were sensitized according to one of two protocols, each used in roughly one-half the challenges. Each monkey was employed for testing 3 times over a 6- 7-month period.

Where the same antigen was used twice in an animal, at least 3 months separated tests. Only one antigen was used in any testing session.

In the first protocol, the monkeys were sensitized 24 and 4 hr prior to challenge with 0.1 ml intradermal injections of serum undiluted, diluted 1: 10, and diluted 1: 2 and heated to 56” C for 2 hr. The heated serum was diluted with an equal volume of saline to prevent gelling, which otherwise sometimes occurred.

In the second protocol, the monkey skin sites were sen- sitized 24 hr, 4 hr, and 2 hr prior to challenge with undiluted serum and 4 and 2 hr prior to challenge with serum diluted 1 : 2 and heated to 56” C for 2 hr. Additional sites were also injected with serum from an individual with negative im- mediate skin test reactions to the allergen being employed in the PCA test. This site was injected 2 hr prior to challenge.

Evans blue dye, OS%, was injected intravenously until the mucous membranes showed definite bluing (usually 12 ml for a 7.5kg animal). The antigen was then injected slowly intraveneously over a 5- 7-min period until bluing at

266 Nelson and Branch J. ALLERGY CLIN. IMMUNOL.

OCTOBER 1977

TABLE I. Homocytotropic antibodies in experimental animals’

W Ww IgE me RAST titer *

Serum concentration Mast cell binding Heating 56” C Optimal sensitization

High Weak Stable Several hours

Low Strong Labile 24 hours

TABLE II. Relation monkey PCA to total serum IgE

Serum IgE (U/ml) Sera*

Total IgES Tested testst antibody

<65 38 66-154 45

155-299 49 300-999 76 >l,ooo 33

241

32 37 4 (12%) 34 40 15 (38%) 32 36 20 (56%) 30 33 21 (64%) 21 23 19 (83%)

149 169 79 (47%)

*Sera are from those patients with at least one 4+ prick test on routine allergy skin testing.

t Two PCA tests were performed with 20 of the 149 sera, resulting in 169 total tests.

$IgE indicates number and percent of sera positive at the 24-hr site.

the sensitized sites was first observed. Approximately 50% additional antigen was then injected and the monkey was observed for 20 to 30 min until no further development of skin reactions occurred. (An example of a monkey PCA is shown in Fig. 1.)

Antigens

The antigens employed were: June grass (Pea prarensis) freeze-dried (Greer Laboratories, Lenoir, N. C.), 1.3 to 3.0 million protein nitrogen units (PNU) in 87 tests; Russian thistle (S&o/a pestifer) freeze-dried (Greer), 865,000 PNU in 27 tests; cat dander (Greer), 50 ml of 1: 10 w/v in 21 tests; Alternaria (Greer), 50 ml of 1 : 10 w/v in 17 tests; and house dust (Greer), 50 ml of 1: 10 fortified with Der- matophagoides farinae (Hollister-Stier Laboratories, Spokane, Wash.), 10 ml of 1: 100 w/v in 17 tests.

Radioallergosorbent test (RAST)

RAST testing was performed with materials obtained from commercial sources (Pharmacia Diagnostics, Piscata- way, N. J.). RAST results were expressed in two ways: (1) 0 to 4+ according to the grading method recommended by Pharmacia, comparing the results to their standard Birch- sensitive reference sera (0 indicating less reactivity than reference serum D, 1 + indicating reactivity between refer- ence serum D and C, 2+ indicating reactivity between ref- erence serum C and B, 3+ indicating reactivity between reference serum B and A, and 4+ indicating greater reactiv- ity than reference serum A); (2) in the second method RAST

TABLE Ill. Relation monkey PCA to RAST for same allergen

Results PCA 0 l+ 2+ 3+ 4+ Mean titert

Positive 2 2 19 45 10 57% Negative 32 17 33 8 0 18%

*RAST titer determined by comparison to Phannacia reference sera.

t Mean titer is percent of anti-IgE bound compared to Phannacia reference serum A.

TABLE IV. Relation monkey PCA to allergen

Allergen Positive

PCA Negative

PCA Percent positive

June grass Russian thistle Cat dander House dust mite Altemaria

35 52 40% 15 12 56% 10 11 48% 8 9 47%

11 6 65%

activity was expressed as a percentage representing counts bound with the tested serum divided by counts bound with reference serum A, multiplied by 100.

RESULTS

The results of PCA testing with sera from patients with positive skin tests to common allergens are summarized in Table II. Forty-seven percent of all PCA tests demonstrated an antibody with the charac- teristics of IgE, i.e., a heat-labile antibody with greater skin sensitization at 24 hr than at 2 or 4 hr. There was no instance in which an antibody with the characteristics of the IgG short-term sensitizing anti- body was found. All test sites that were positive at 2 or 4 hr had larger areas of bluing at 24 hr. In the one instance when activity was not completely destroyed by heating, reactions were present with heated serum at both 4 and 24 hr, and the 24-hr reaction to unheated serum was the largest, indicating incomplete inactiva- tion of a long-term sensitizing antibody. There was no evidence of declining reactivity with repeated testing of the monkeys. In the first round of tests, 43% of sera were positive, in the second round 42% were positive, and in the third round of testing 50% of sera gave positive PCA tests.

The incidence of tests indicating the presence of IgE-like antibody (‘ ‘IgE’ ‘) increased with rising levels of total serum IgE. In those patients with a total serum IgE of less than 65 U/ml, only 12% of tests were positive for ‘ ‘IgE”, while in those with serum IgE over 1,000 U/ml the incidence of positive tests

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for specific “IgE” by PCA in monkeys was 83%. Sensitivity in detecting ‘ ‘IgE” varied from monkey

to monkey and also from test to test in the same monkey. Nevertheless, the detection of specific ‘ ‘IgE”’ by monkey PC.4 testing showed correlation with RAST testing for IgE antibodies to the same antigen in the same serum (Table III).

The incidence of positive PCA tests for “IgE” did not vary significantly by chi-square testing with the antigen employed in the test (Table IV).

DISCUSSION

Our study, which employed techniques similar to those used by others to demonstrate the presence of IgG short-term sensitizing antibody, failed to demon- strate the presence of antibodies of this type in any of the 149 sera tested. Antibody with the characteristics of IgE was demonstrated in only 47% of sera tested. This relatively low incidence of positive tests for IgE was not unexpected, since monkey skin has been shown to be less sensitive than human skin to sensiti- zation with human IgE. la Our frequency of demon- strating specific “IgE” by this technique is not con- spicuously lower than that reported by others using a similar method.i

The most extensive studies of the occurrence of the human IgG heat-stable short-term skin-sensitizing antibody are those by Parish.’ In a total of 359 sera tested by PCA in monkeys, IgG S-T S antibody was present in 19 (5%). Although he did report that 1 of ?8 grass-sensitive patients had the Ig S-T S antibody, in the majority the IgG S-T S antibody sensitivity was not directed toward inhalant allergens. Milk, strep- tococcal antigens, horse serum and tetanus toxoid ac- counted for 16 of Parish’s cases. Parish also has re- ported that sera containing the IgG S-T S antibody usually also contain precipitins for the same antigen.’

Bryant, Bums, and Lazarus,15, l6 on the other hand, reported on studies in a group of patients with allergic bronchial asthma and positive prick tests to Dermatophgoides pteronyssinus. The sera of 2 1 of a group of 49 patients were tested by PCA in monkeys, employing the same strain of monkey (Macaca nemestrina) and technique of challengeI as employed in our study. Eight were found to have only the IgG S-T S antibody, and 2 of the 13 with IgE antibody also had the heat-stable S-T S antibody.15 Bryant and as- sociates reported that a total serum IgE level of 400 U/ml separated the two groups. Those having an IgE level higher than 400 U/ml had IgE antibody to D. pteronyssi;ilus, while those having an IgE level below 400 U/ml had, with only one exception, the IgG S-T S antibody. l5 We, however, did not note any abrupt

IgG short-term sensitizing antibodies 269

change in incidence of demonstrable “IgE” an- tibodies at any particular level of total IgE, but rather a continuous change in incidence from 12% in the group with lowest IgE levels to 83% in those with levels above 1,000 U/ml.

It is presumed that most or all of the antibody that we detected in our study and that was heat-labile and sensitized monkey skin maximally at 24 hr was IgE. However, no adsorption studies with anti-IgE were performed, and there are a few reports which suggest that skin-sensitizing antibodies that are heat-labile and sensitize the skin for long periods of time may occasionally occur in the IgG subclasses.lg, 2o We cannot, therefore, exclude the participation of such an antibody in our results. The relatively heat-stable antibody that was detected in one serum in our study does not necessarily indicate a non-IgE antibody. This serum did produce greater sensitization at 24 hr at the site sensitized with unheated serum than at any other, and classic reagins have been reported to be heterogenous in response to heating, requiring up to 7 hr for complete inactivation.21

The failure to demonstrate the IgG short-term skin-sensitizing antibody in this study should not be construed as arguing against the existence of such a homocytotropic antibody in man, since its occurrence is well documented. It does, however, suggest that this class of skin-sensitizing antibody does not play a major role in allergy to common inhalants.

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