In vitro assays of drug-specific IFN-γ and IL-4 production offer potential for use as rapid diagnostic tests. Cytokine detection offers distinct advantages over the LPA, including a shorter assay time, a greater sensitivity and effectiveness in testing immunosuppressed patients.

Ultraviolet-B-induced erythema (one, two, or four times the minimal erythema dose) was reduced but not abolished by application of 1% indomethacin gel immediately after irradiation of human skin. Continuous synthesis of prostaglandins is reflected by similar levels of indomethacin-mediated inhibition of erythema at any time within 48 h after irradiation. Repeated applications of indomethacin did not increase the inhibition. Twenty-four hours after irradiation with four minimal erythema doses, mean prostaglandin E2 levels in suction blisters were 27.2 ng per ml (SEM 11) compared with 8.6 ng per ml in unirradiated skin (n = 25; p < 0.01). Prosta glandin E2 levels in dermal tissues, sampled by microdialysis (depth 0.6 +/- 0.1 mm), were 310 pg per ml (SEM 123) and 237 pg per ml (SEM 88) in irradiated and unirradiated skin, respectively (n = 7, n.s.). Nitric oxide also made a significant contribution to ultraviolet-B-induced erythema. Ultraviolet erythema was inhibited by L-NAME in a dose-related fashion with 2 mM L-NAME causing total abolition of the response. L-NAME was effective at all time points up to 48 h suggesting that NO was produced continuously. NO was undetectable in suction blister fluid but in dermal microdialysate NO was present at 44.3 ng per ml (SEM 6.2) following ultraviolet B compared with 26.0 ng per ml (SEM 8.0) in unirradiated skin (p < 0.05), approximately 1000 times the molar concentration of prostaglandin E2. These findings confirm prostaglandin E2 and NO to be mediators of ultraviolet-induced erythema. They also show that there is prolonged synthesis of both mediators within the erythemal response and that synthesis of NO is induced by lower doses of ultraviolet B compared with that of prostaglandin E2.

The 'old favourites' used for treatment of inflammatory diseases, and hence, the original immunomodulators, include the glucocorticoids, azathioprine, methotrexate and hydroxyurea. Glucocorticoids are still one of the most effective anti-inflammatory agents because they work on several different intracellular processes and hence, block many components that contribute to inflammatory and immune responses. They bind to intracellular glucocorticoid receptors which transport them into the nucleus. Here the receptor/steroid complex may bind to many genes that interact with transcription factors including NFkappaB and AP-1, to inhibit their activation, thereby preventing activation of many genes encoding immune effector and pro-inflammatory cytokines. Also, protein kinases involved in intracellular signalling, are directly activated resulting in phosphorylation of various targets of which Annexin (AXA)-1 is critical in inhibiting biosynthesis of both purines and DNA. This results in reduced proliferation of B and T lymphocytes, reduced immune effector mechanisms and reduced recruitment of mononuclear cells including monocytes into sites of immune inflammation. Methotrexate also blocks DNA synthesis and hence cellular proliferation but also induces release of adenosine. This inhibits chemotaxis of polymorph neutrophils and release of critical cytokines such as TNF-alpha and Interleukins 6 and 8. Hydroxyurea also inhibits DNA synthesis with inhibitory effects on proliferation of lymphocytes and possibly kerationcytes. Even though many new agents with much greater selectivity are coming through into clinical use, this group of old agents still have an absolutely central position in the therapeutic armamentarium. Their value lies in the fact that they are not 'clean' drugs with narrow effects but they inhibit a wide range of mechanisms involved in immune and inflammatory processes.