Desensitization of experimental contact sensitivity

Hapten-induced contact hypersensitivity, autoimmune reactions, and tumor regression: plausibility of mediating antitumor immunity

Haptens are small molecule irritants that bind to proteins and elicit an immune response. Haptens have been commonly used to study allergic contact dermatitis (ACD) using animal contact hypersensitivity (CHS) models. However, extensive research into contact hypersensitivity has offered a confusing and intriguing mechanism of allergic reactions occurring in the skin. The abilities of haptens to induce such reactions have been frequently utilized to study the mechanisms of inflammatory bowel disease (IBD) to induce autoimmune-like responses such as autoimmune hemolytic anemia and to elicit viral wart and tumor regression. Hapten-induced tumor regression has been studied since the mid-1900s and relies on four major concepts: (1) ex vivo haptenation, (2) in situ haptenation, (3) epifocal hapten application, and (4) antigen-hapten conjugate injection. Each of these approaches elicits unique responses in mice and humans. The present review attempts to provide a critical appraisal of the hapten-mediated tumor treatments and offers insights for future development of the field.

Prevention of nickel-induced allergic contact reactions with pentoxifylline

In this study, we investigated the effect of pentoxifylline, an inhibitor of TNF-alpha, on the contact sensitivity response induced by nickel. For induction, open epicutaneous sensitization by NiSO4. 6 H2O (25% aq.) solution was applied on the backs of 38 albino guinea pigs 5 days a week for 4 weeks. NaCl (0.9%) solution was applied epicutaneously to 10 albino guinea pigs as a control group. 19 were sensitized by nickel and developed positive patch test reactions. Patch tests were repeated after 10 of the sensitized pigs were given pentoxifylline 20 mg/kg/day orally. At the end of this study, only 2 positive patch test reactions were observed in the pentoxifylline-treated group, while 7/9 of the untreated guinea pigs developed positive reactions. These results suggest that pentoxifylline inhibits the contact sensitivity response induced by nickel only during drug administration.

Inhibition of delayed hypersensitivity reactions in mice by colchicine. I. Mechanism of inhibition of contact sensitivity in vivo

Colchicine has been recently shown to inhibit delayed hypersensitivity reactions (DHR). In the present study we investigated the effects of colchicine on contact sensitivity (CS) to dinitrofluorobenzene. Colchicine, at a dosage level of 15 micrograms/mouse, inhibited the elicitation of the contact response only when given on the day of ear challenge. Administration of the drug during the induction phase did not have any effect on the CS reaction. By using adoptive transfer experiments, we could demonstrate that CS was suppressed only when colchicine was given to the recipient mice, while treating the donors of immune lymph node cells (I-LNC) did not affect their ability to transfer a significant DHR. These findings were observed also when I-LNC were directly injected into the ears, a result which indicated that there was no effect of the drug on the ability of effector cells to migrate to the site of antigen challenge. Neither was there any effect on the distribution of T cell subsets in peripheral lymph nodes. The proliferative response of LNC to antigenic or mitogenic stimulation in vivo or in vitro was also not affected by colchicine pretreatment. These findings raise major questions about the mechanism of action of colchicine in vivo and suggest that more experimentation is required to probe the mechanism of colchicine-induced suppression of DHR.

Hyposensitization to poison ivy after working in a cashew nut shell oil processing factory

19 adults were patch tested to urushiol, the allergen in poison ivy/oak, to determine their sensitivity to this allergen after working in a cashew nut shell oil (CNSO) processing plant. The cashew nut tree and poison ivy/oak are in the same botanical family. Anacardiaceae, and they share similar chemicals which cause allergic contact dermatitis. 13 of the 19 workers had a preemployment history of poison ivy sensitivity, with 10 developing CNSO dermatitis. After working in this factory for several months, 9 of the 13 noticed a decreased sensitivity or no sensitivity to poison ivy/oak. When tested to urushiol extract, only 3 reacted positively, 2 minimally. These results imply that hyposensitization to poison ivy/oak occurred in these employees after development of hardening to cashew nut shell oil.