Clinical and mechanistic differences between FK506 (tacrolimus) and cyclosporin A

Quantification of the influence of mycophenolic acid on the release of endothelial adhesion molecules

BACKGROUND

Mycophenolic acid selectively inhibits inosine 5'-monophosphate dehydrogenase leading to a shortage of guanosine nucleotides. Since GTP is required for the synthesis of glycoproteins, this immunosuppressive drug also influences the production of several cell adhesion molecules.

METHOD

Soluble endothelial cell adhesion molecules released into cell culture supernatants after an incubation period of 16 h are assessed via a standard ELISA procedure applying test kits for E-selectin, VCAM-1 and ICAM-1.

RESULTS

Treatment with TNF-alpha leads to the induction of E-selectin and causes a significant increase in VCAM-1 and ICAM-1 content in the supernatant in relation to the level of unstimulated cells. Due to the inhibitory effects of MPA-applied either alone or in combination with cyclosporin A and prednisolone-sE-selectin is significantly reduced and sVCAM-1 is slightly but not significantly decreased, whereas sICAM-1 levels remain unchanged.

CONCLUSIONS

We demonstrate that the influence of MPA on endothelial cell adhesion molecules can readily be determined via ELISA. The results indicate that the immunosuppression by MPA is also achieved by slightly reducing the expression and consequent release of E-selectin, a pivotal molecule in the first step of leucocyte-endothelial interactions.

Inhibition of cytokine production and cytokine-stimulated T-cell activation by FK506 (tacrolimus)1

Insofar as it exerted its immunosuppressive effect by inhibiting cytokine expression, we assessed the effect of FK506 (Tacrolimus) on cytokine-stimulated T-cell activation. Human T cells, treated with FK506, or controls were stimulated with the mitogens PHA + PMA, Con A, and the "CD3-bypass" stimulation regimen, PMA + ionomycin. T-cell proliferation was quantitated by measuring the uptake of tritiated thymidine, and mRNA expression was assessed by RT-PCR. FK506, in a concentration-dependent fashion, inhibited T-cell proliferation and steady-state mRNA expression of IL-2 and IL-7; half-maximal suppression was obtained at 10(-7) to 5 x 10(-8) M. We tested whether FK506 antiproliferative effect could be overcome with exogenously reconstituted rIL-2 and/or rIL-7. Neither rIL-2 nor rlL-7, individually in conjunction with suboptimal concentrations of PHA or Con A, or in combination without any costimulus, was capable of abrogating FK506 antiproliferative effect, indicating that FK506 also acted by inhibiting cytokine-stimulated T-cell activation. To confirm this, T cells were treated with FK506 and stimulated by rIL-2 and rIL-7, individually in conjunction with suboptimal concentration of PHA and Con A. In addition, T cells were stimulated with rIL-2 and rIL-7 without any costimuli. FK506 inhibited T-cell activation stimulated by rIL-2 and by rIL-7, individually and in combination. This confirms that, in exerting its antiproliferative effect, FK506 acts at two levels, by inhibiting cytokine availability and by suppressing cytokine effect on target cells, and explains the beneficial effect of FK506 in attenuating ongoing immune responses.

Phaeohyphomycosis caused by Alternaria infectoria in a renal transplant recipient

We report on a case of phaeohyphomycosis caused by Alternaria infectoria in a renal transplant recipient with pulmonary infiltrates and multiple skin lesions. Diagnosis was based on microscopy and culture of the skin lesions. Treatment consisted of a combination of surgical excision and systemic antifungal therapy, first with itraconazole and subsequently with liposomal amphotericin B, for 39 days. At a 20-month follow-up visit, no recurrence of the skin lesions or the pulmonary infiltrates had occurred.