Chapter 7: Immune-Mediated Tissue Injury

INTRODUCTION

The goal of the immune system is to protect the body from anything that is not a part of it, from germs to foreign bodies to harmful substances. The exquisite process of immunology begins in the skin with cells that phagocytose bacteria (macrophages, polymorphic neutrophilic lymphocytes), cells that release cytokines (endothelial cells, activated platelets, neutrophils, and T-lymphocytes), and dendritic cells that carry antigens from the injury site to the local lymph nodes where the adaptive immune system is activated.¹ If the immune system is over-activated, the body will attack itself and destroy healthy cells and tissues; if it is suppressed, the body becomes susceptible to microbes that are normally destroyed and therefore it develops infections more easily.² While a discussion of this miraculous process is beyond the scope of this chapter, it is important to recognize that both the up- and down-regulation of the immune system and its processes can result in dermal wounds, or they can impede the healing of existing wounds through a change in cellular activity or as a result of the medication used to treat the disorder. The purpose of this chapter is to assist the clinician in recognizing wounds that are mediated by immune disorders, as well as to stress the importance of understanding the effects of medications (e.g. corticosteroids, NSAIDs, anti-rejection medications, and other immune-suppressors) on the wound healing process, in which case collaboration between the wound care clinician and the immunologist is needed to manage the medications in such a way that wound healing is optimized.

HYPERSENSITIVITY SYNDROMES

An allergic reaction can be either contact (the offending substance comes in direct contact with the skin) or systemic (the offending substance is either injected or ingested). In either case, the offending substance is lysed or broken down by the macrophages and polymorphic neutrophilic lymphocytes (PMNs), and the resulting antigens (anti- body generators) are presented to the host immune system T cells, thereby activating the complex immune response. Reactions can vary from mild to life-threatening, and will usually increase in severity with multiple exposures to the offending agent. The first treatment of any allergic reaction is to identify and stop use of the offending substance. Table 7-1 lists common agents for both allergic contact dermatitis and irritant contact dermatitis, and Table 7-2 lists medications that are most commonly reported to cause drug-induced hypersensitivity syndromes.