Equine and Livestock Immune System Modulators

Gross Lesion Examples
Microscopic Examples

Pathogenesis: Loss of cohesion between keratinocytes which is referred to as acantholysis. Breakdown of intercellular attachments can occur via immunologic attack (pemphigus) or as a result of enzymatic destruction such as in a pyoderma. Acantholysis will lead to formation of a vesicle, bullae, cleft or pustule at some level of the epidermis.

Divided into intraepidermal or subepidermal patterns

Level of the epidermis where lesion occurs and type/number of inflammatory cells presents help to narrow differential.

Intraepidermal Vesicular/Pustular Dermatitis

Description:

Histological lesions:
Vesicles, bullae, or pustules are in the epidermis. These "blister" like lesions may be fluid filled, or contain varying numbers of neutrophils, eosinophils, or possibly acanthocytes.

Gross lesions: Clinically, tiny to several centimeter in size blister-like lesions are present. Pustules are yellowish, while vesicles or bullae may contain clear, serous fluid. These are considered the primary lesions and are very fragile, hence more often you will see the lesions present as crusts - what remains after the lesion ruptures. If the epidermal separation is at a deep level, you can see erosions and ulcerations.

Suggested conditions:

Subcorneal vesicle/pustule:
1. Superficial pyoderma - PMNs
2. Pemphigus foliaceus - PMNs or EOS
3. Pemphigus erythematosus - PMNs or EOS
4. SLE (feline) - PMNs
5 . Ectoparasites/allergies - EOS

Suprabasilar acantholysis - separation just above the basal layer. Basal cells remain on floor of vesicle as row of "tombstones".

1. Pemphigus vulgaris -

Subepidermal Vesicular/Pustular Dermatitis

Pathogenesis: Immune mediated and enzymatic destruction of the basement membrane components; genetic defects in structural components of the basement membrane, physical damage to the basement membrane.

Description: The entire epidermis is separated from the dermis.

Suggested conditions: 1. Severe lichenoid dermatoses(see above): SLE 2. Mechanobullous diseases: epidermolysis bullosa 3. Thermal burns 4. TEN 5. Bullous pemphigoid

Gross lesion examples from a horse with pemphigus foliaceous. From a distance we can see he has large areas of alopecia. A closer view reveals many primary lesions consisting of fragile vesicles corresponding to the microscopic lesions depicted in the first slide from this case.

Clinical Photo 1: Whole body view

Clinical Photo 2: Close view

Microscopic example given is skin from a horse with pemphigus foliaceous.
Low Power
High Power
Positive Immunofluorescence.

Note: in the lower magnification the subcorneal pustule containing neutrophils and a few acanthocytes. The surface of the pustule is just the fragile stratum corneum. You can see why the fragile pustules are usually transient and give way to the more commonly encountered secondary lesion of a crust.

Note: in the higher magnification, many acantholytic keratinocytes which appear as large, polygonal eosinophilic cells amidst the PMNs. This is an example of a type II hypersensitivity disease. Auto-antibody deposition can be detected via special procedures such as immunoperoxidase staining or immunofluorescence.