Cytotoxic T lymphocytes and phenotypically abnormal epidermal dendritic cells in fixed cutaneous eruptions

Immune response to xenobiotics in the skin: from contact sensitivity to drug allergy

Skin is the most frequent target of adverse drug reactions. These cutaneous drug reactions (CDRs) show varied clinical manifestations ranging from mildly discomforting rashes to life-threatening Stevens-Johnson syndrome or toxic epidermal necrolysis. Most CDRs appear to be immune mediated, although the mechanism by which they are initiated remains unclear. In this review, current knowledge of the mechanisms by which xenobiotics provoke immune responses in the skin after epicutaneous administration and how similar reactions may occur after systemic routes are summarised. This review also discusses a variety of genetic or environmental factors that may determine the susceptibility of individuals towards immune responses in skin following drug exposure.

Mechanisms of drug eruptions: Part I

The pathogenetic mechanisms underlying common, and less common but severe, adverse cutaneous drug reactions are reviewed. Pharmacogenetic variability may account for a susceptibility to serious drug reactions to sulphonamides and anticonvulsants, as well as to lupus erythematosus (LE)-like syndrome. Exanthematous drug reactions may have an immunological basis. Cell mediated cutaneous drug reactions, including lichenoid reactions, LE-like syndrome, fixed drug eruption, erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis, will inevitably involve elements of the skin immune system. Graft-versus-host disease provides a useful model for aspects of these drug-induced disorders. Urticaria, angioedema, anaphylaxis and anaphylactoid reactions may involve Type I immunoglobulin (Ig)-mediated or Type III hypersensitivity, or may be caused by pharmacological, non-allergic means. Drug-induced vasculitis, serum sickness and the Arthus phenomenon are manifestations of the immune complex disease. Drug-induced pemphigus may involve immune dysregulation, but several thiol-containing drugs are able to cause antibody-independent acantholysis directly.

Antigen processing: the gateway to the immune response

The T-lymphocyte response to an antigen is governed by the source of that antigen and the way in which it is processed. Before recognition by T lymphocytes, proteins must be degraded to peptides by antigen-presenting cells. The peptides are then presented on major histocompatibility complex (MHC) molecules for recognition by the T cells. Antigens arising outside the cell (e.g., bacteria) are phagocytosed and processed by the exogenous pathway for presentation on MHC class II molecules (e.g., DR) to CD4+ cells. Antigens derived from the cytoplasm (e.g., viral proteins) are processed by the endogenous pathway for presentation by MHC class I molecules (e.g., HLA-A, -B, -C) to CD8+ cells. The response to a hapten or drug is a function of the antigen processing pathway and is determined by its chemical properties. Antigen processing also governs the T-cell response to pathogens, vaccines, and autoimmune conditions.

Fixed drug eruptions: evidence for a cytokine-mediated process

Fixed drug eruptions (FDE) are immunologic reactions to drugs which produce erythematous plaques or blisters that characteristically recur at the same cutaneous sites with repeated antigenic challenges. While a detailed pathogenesis of these lesions remains obscure, T-lymphocyte infiltration has been documented repeatedly. In this study, we tried to determine if FDE were mediated, at least in part, by cytokines, such as gamma-interferon. We examined biopsies from 6 cases of clinically well-documented FDE with an HLA-DR antibody, LN3, and an antibody to gamma IP-10 (IP-10), a protein expressed by keratinocytes, monocytes, lymphocytes and endothelial cells following exposure to gamma-interferon. We found staining of the dermal lymphocytes with anti-HLA-DR antibody in all 6 cases examined. Keratinocytes and endothelial cells showed only focal staining at the antibody concentrations used. In addition, there was keratinocyte staining with the IP-10 antibody at all levels of the epidermis, with accentuation in areas of blister formation. There was more intense staining of keratinocytes with the IP-10 antibody in cases with accumulations of HLA-DR positive lymphocytes in the dermis. We believe that these findings are consistent with the hypothesis that FDE represent cell-mediated immunologic responses to a variety of antigens, and further, that the histologic alterations can be explained, at least in part, by a cytokine-mediated process.

Drug-induced skin reactions and acute cutaneous graft-versus-host reaction: a comparative immunohistochemical study

Skin biopsies from eight patients with drug-induced dermatitis have been compared with skin biopsies from 16 patients developing skin lesions (acute graft versus host-reaction and/or drug-induced reaction) after bone marrow transplantation. Biopsies were investigated using immunohistochemistry and several monoclonal antibodies. Morphological and immunohistochemical patterns in skin biopsies of both groups were very similar. The only difference seen was a reduced number of epidermal Langerhans cells with poorly developed dendrites in skin biopsies taken from patients who underwent bone marrow transplantation. If the latter finding is due to the cytotoxic drug regimen administered before bone marrow transplantation, as previously stated, we doubt the usefulness of skin biopsies in the differential diagnosis of acute graft-versus-host reaction and drug-induced skin lesions.