Immunology of the Fungal Diseases

Rebecca A. Cox

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9781000141849
• Edition: 1
• Topic: Medicine
• Subtopic: Immunology

This informative text is divided into eight chapters, each of which presents a comprehensive review of natural and acquired host defense mechanisms in a major mycotic disease. The chapters are written by distinguished scientists whose studies have contributed significantly to the understanding of the immunology of the mycoses. This text should provide a valuable reference for researchers, practicing clinicians, and new investigators entering this expanding field.

Chapter 1

DERMATOPHYTOSIS

Peter G. Sohnle

TABLE OF CONTENTS

I. Introduction

A. Overview

B. The Dermatophytes

C. Clinical Forms of Dermatophytosis

D. Dermatophytids (Id Reactions)

E. Predisposing Factors

1. Cutaneous Factors

2. Systemic Factors

II. Natural Resistance

A. Nonimmunological Cutaneous Defenses

B. The Inflammatory Response

1. The Relationship between Inflammation and Chronicity

2. The Pathology of Dermatophytosis

3. Chemotactic Mechanisms

III. Acquired Resistance

A. Immunological Mechanisms in the Skin

1. General Characteristics

2. The Epidermal Langerhan’s Cells

3. Epidermal Cell-Derived Thymocyte-Activating Factor

B. Immunity to Reinfection

1. Experimental Infections in Animals

2. Experimental Infections in Humans

C. Antigens of the Dermatophytes

1. Antigenic Composition

2. Cross-Reactivity of Dermatophyte Antigens

D. Humoral Immunity

1. Immunoglobulin

2. Immediate Hypersensitivity

E. Cell-Mediated Immunity

1. Delayed Hypersensitivity

2. In Vitro Correlates of Cell-Mediated Immunity

IV. Immunomodulation

A. Mechanisms of Immunosuppression

1. Evidence for Active Suppression of Cell-Mediated Immunity

2. Antagonism between Immediate and Delayed Hypersensitivity

B. Augmentation of Immune Responses

1. Trichophytin as a Vaccine or a Therapeutic Agent

2. Inhibition of Immediate Hypersensitivity to Trichophytin

3. Other Methods of Restoring Cell-Mediated Immunity to Trichophytin

4. Potential for the Use of Immunomodulatory Therapy in Dermatophytosis

V. Summary

Reference

I. INTRODUCTION

A. Overview

Dermatophytosis is the infection of keratinized structures, including the hair, nails, or stratum corneum of the skin, by organisms of three genera of fungi termed the dermatophytes. The latter are well adapted to this specialized site and therefore differ from most other pathogenic fungi in that they are not opportunists. There are other types of superficial fungal infections, as shown in Table 1. Dermatophytosis, superficial candidiasis, and tinea versicolor are the most common cutaneous mycoses, especially in temperate climates. Chronic superficial Candida albicans infections (chronic mucocutaneous candidiasis) are quite rare and generally occur in patients with some kind of underlying immunological defect. In contrast, chronic tinea versicolor is quite common in otherwise healthy persons, especially in warm climates. Tinea versicolor is a mild, noninflammatory condition with minimal symptoms, whereas chronic mucocutaneous candidiasis is a serious, often disfiguring condition generally requiring aggressive therapy. In comparison, dermatophytosis seems to produce a much wider range of cutaneous manifestations than either cutaneous candidiasis or tinea versicolor. Dermatophytosis can vary from minimally inflammatory infections, which are often quite chronic, to severely inflammatory infections, which fortunately are generally self-limited. In dermatophytosis, the vigor of the host's response to the invading organism seems to be directly related to the rate at which the infection can be cleared. Patients with chronic forms of dermatophytosis are the most likely to show deficient immunological responses against the infecting organism. The factors mediating host defenses of the skin against superficial fungal infections are complex and appear to differ somewhat from those operative elsewhere in the body. In this chapter, we will discuss the available information on mechanisms of defense against the dermatophytic fungi in relation to the clinical characteristics of this condition. In addition, we will also review the data that exist on immunomodulation in dermatophytosis and discuss the potential of this form of therapy in these infections.

B. The Dermatophytes

There are three genera of dermatophytes: Trichophyton, Microsporum, and Epidermophyton. In addition, the discovery of the perfect or sexual reproductive stage of several dermatophytes has resulted in the reclassification of these species into the two new genera of Arthroderma (the perfect Trichophyton species) and Nannizzia (the perfect Microsporum species). Whereas Trichophyton, Microsporum, and Epidermophyton species are classified in the subdivision Deuteromycotina, the two genera of perfect species are classified within the subdivision Ascomycotina. The latter also contains the etiologic agents of blastomycosis and histoplasmosis.

Table1
SUPERFICIAL FUNGAL INFECTIONS

Infection	Responsible organism(s)	Site(s) of infection
Dermatophytosis	Species of Trichophyton, Epidermophyton, Microsporum	Skin, hair, nails
Superficial candidiasis	Candida albicans	Skin, nails, mucous membranes
Tinea versicolor	Pityrosporum orbiculare (Malassezia furfur)	Skin
Tinea nigra	Exophiala werneckii	Skin
Black piedra	Piedraia hortae	Hair
White piedra	Species of Trichosporon	Hair
Fungal keratitis	Species of Fusarium	Cornea

Table2
CLASSIFICATION OF MAJOR DERMATOPHYTE SPECIES BY RESERVOIR

Anthropophilic	Zoophilic	Geophilic
Trichophyton rubrum	Trichophyton mentagrophytes var. mentagrophytes	Trichophyton terrestre
Trichophyton mentagrophytes var. interdigitale		Trichophyton ajelloi
	Trichophyton verrucosum	Microsporum gypseum
Trichophyton tonsurans	Microsporum canis	Microsporum vanbreuseghemii
Trichophyton schoenleini
Trichophyton violaceurm
Trichophyton concentricum
Microsporum audouini
Epidermophyton floccosum

There are at least 40 species recognized by taxonomists in the three genera of dermatophytes. These species appear to be relatively similar microbiologically, although they can be differentiated on the basis of colonial morphology, microscopic appearance (particularly the structure of macroconidia and microconidia), and some biochemical tests. The many species of dermatophytes have certain other differences, including their reservoirs, the cutaneous sites usually infected, the degree of inflammation generally produced, and the chronicity of their infections. An unusual and important characteristic of this group of microorganisms is their ability to digest keratin. They can therefore infect the stratum corneum, hair, and nails using keratin as a source of nutrients.

The dermatophytes can be classified as anthropophilic (found mainly in humans), zoophilic (found mainly in animals), or geophilic (found mainly in the soil). Some of the major species in each group are shown in Table 2. This classification is important because the groupings determine not only the major reservoirs for these species, but also to some degree the clinical characteristics of the infections caused by these organisms. The anthropophilic species tend to produce less inflammatory and more chronic infections than do the zoophilic and geophilic species. This characteristic suggests that the anthropophilic species are better adapted to the human host than are the species in the other two groups. Even so, the anthropophilic species are probably not part of the normal flora in the majority of humans. For example, fungal cultures of uninfected feet reveal isolates of dermatophytes only rarely.^1,2 The dermatophytes, therefore, differ from the two other major causes of superficial fungal infections in humans in that C. albicans and Pityrosporum orbiculare are normal human flora, of the gastrointestinal tract³ and skin,⁴ respectively.

Table3
TYPES OF DERMATOPHYTOSIS

Condition	Site	Organisms	Special characteristics
Tinea pedis	Feet	T. rubrum, T. mentagrophytes	Secondary bacterial infections often occur
Tinea cruris	Groin	E. floccosum, T. rubrum	Most cases occur in males
Tinea corporis	Aims, legs, torso	T. rubrum, T. mentagrophytes, T. concentricum (tinea imbricata), M. canis	Classical ringlike lesions can occur on glabrous skin
Tinea barbae	Beard	T. rubrum, T. verrucosum	Zoophilic organisms can cause inflammatory infections of the beard area
Tinea unguium	Nails	T. rubrum, T. mentagrophytes, E. floccosum	Very difficult to eradicate
Tinea capitis	Scalp	T. tonsurans, M. audouini, M. canis	Severe inflammatory reaction called a kerion can occur
Tinea favosa (favus)	Scalp, torso	T. schoenleini	Conspicuous feature is a thick, yellow crust (scutulum)

C. Clinical Forms of Dermatophytosis

The first report of dermatophytosis was by Aulus Cornelius Celsus, who described an inflammatory scalp infection about 30 A.D.⁵ The term “tinea” was used early on to describe these infections because of the similarity of the effect...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• The Editor
• Contributors
• Table of Contents
• Chapter 1 Dermatophytosis
• Chapter 2 Aspergillosis and Mucormycosis
• Chapter 3 Candidiasis
• Chapter 4 Cryptococcosis
• Chapter 5 Blastomycosis
• Chapter 6 Coccidioidomycosis
• Chapter 7 Histoplasmosis
• Chapter 8 Paracoccidioidomycosis
• Index