Cellular or delayed-type hypersensitivity (DTH) can be assessed by intracutaneous testing with bacterial, viral and fungal antigens to which most healthy persons are sensitized. A positive skin test denotes prior antigenic exposure, T-cell competency and an intact inflammatory response (1,2). The reaction usually peaks 48 hours after antigen is introduced into the skin and is manifest as induration at the test site.

Recall antigens may be useful in evaluating delayed-type hypersensitivity by eliciting positive induration reactions 48 to 72 hours after intracutaneous administration. Except for mumps skin test antigen, most commonly used recall antigens were developed for other purposes, and the size of the reaction elicited may not be directly related to cellular immunity because of variability in antigen source and dose and skin test administration and measurement techniques. Useful antigens are those which elicit a reaction size ≥5 mm in more than 50% of normal individuals. The combination of results from skin testing with more than one antigen should result in detection of DTH in at least 95% of normal subjects (2).

The inflammatory response associated with the DTH reaction is characterized by an infiltration of lymphocytes and macrophages at the site of antigen deposition. Specific cell types that appear to play a major role in the DTH response include CD4⁺ and CD8⁺ T lymphocytes which leave the recirculating lymphocyte pool in response to exogenous antigen (3). Both CD4⁺ and CD8⁺ lymphocytes have been recovered from DTH reactions elicited by Candida antigen (4).

In the literature, the incidence of DTH reactions to unstandardized Candida antigens has been reported to vary from 52 - 89%, depending upon the strength of the antigen and the mm induration required for a positive test (5,6,7,8,9).

Published studies have reported that antigens of Candida albicans are useful in the assessment of diminished cellular immunity in persons infected with human immunodeficiency virus (10,11). Responses to DTH antigens have been reported to have prognostic value in patients with cancer (5).

RESPONSE TO CANDIN^® in Healthy Adults (Table1): In one group of 18 subjects, 14 (78%) of the individuals reacted to CANDIN^® with an induration response of ≥5 mm at 48 hours. In a second study of 35 subjects, 21 (60%) had induration reactions ≥5 mm at 48 hours. In this study, 65% of males tested positive compared to 53% of females; the mean induration in responding males was 12.8 mm and in responding females was 13.0 mm. When subjects in these studies were tested with two reagents, CANDIN^® and Mumps Skin Test Antigen, 92% were positive to at least one antigen, a higher response rate than to either antigen used alone (15).

RESPONSE TO CANDIN^® in Adults with HIV Infection: In one study (Table 2). the skin test responses of adults with HIV infection were compared to those of healthy control subjects (age range AIDS 22-65, HIV positive 20 - 45, Controls 25 - 69). When HIV infected subjects were classified by the CDC's 1993 revised classification system for H.I.V infection (12), a significant difference was found between AIDS patients and normal controls in both mean induration (p = 0.01) and proportion with ≥5 mm response (p< 0.01). The responses in HIV-infected patients (without AIDS-indicating conditions or AIDS-indicating CD₄ T-cell counts) were less than in normal subjects, but the differences were not statistically significant.

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