Diseases Involving Cell-mediated Immunity
(Type IV reactions) |  |
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Granulomatous reactions to microorganisms such as mycobacteria,
Coccidioides
,
Blastomyces
, and
Histoplasma
spp
, and possibly feline infectious peritonitis virus, may be due to chronic cell-mediated immune reactions. Although cell-mediated immunity effectively controls these types of infection in most individuals, for poorly understood reasons, these same mechanisms are only partially effective in others. A granulomatous reaction occurs, characterized by a fibrous stroma and an infiltration of macrophages, giant cells, and lymphocytes |
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Lymphocytic choriomeningitis is a viral infection of mice (
Generalized Diseases) in which CNS damage is due to the destruction of virus-infected cells by thymus-derived lymphocytes.
Old-dog encephalitis (
Canine Distemper: Introduction) also may result from cell-mediated immune mechanisms directed against cells persistently infected with canine distemper virus. The initiating canine distemper virus infection is usually clinically inapparent and may precede the encephalitis by years. |
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Contact hypersensitivity results from chemicals reacting with dermal proteins, which modify self-proteins. These modified proteins are antigenic, and the host’s cell-mediated immune response against these chemically altered dermal proteins damages the skin, eg, poison oak and poison ivy reactions in humans. This reaction has been described in both dogs and horses and usually occurs as a result of contact with sensitizing chemicals incorporated in plastic food dishes,
plastic collars, and drugs placed on the skin. |
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Autoimmune thyroiditis has been recognized in dogs and is characterized by destruction of the thyroid gland by an autoimmune process that has both humoral (Type II) and cell-mediated (Type IV) components. The disease is particularly prevalent in Doberman Pinschers, Beagles, Golden Retrievers, and Akitas. Hypothyroidism (
Hypothyroidism) may be the sole manifestation of the disease or may be a clinical or subclinical component of a broader autoimmune
disorder such as systemic lupus erythematosus, idiopathic polyarthritis, immune-mediated meningitis (periarteritis nodosa), panendocrinopathy, and rheumatoid arthritis. |
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Autoimmune adrenalitis has been reported in dogs. The adrenal glands are slowly destroyed by a plasmacytic-lymphocytic infiltrate. When sufficient glandular tissue is destroyed, the dogs develop Addison’s syndrome (adrenocortical insufficiency,
Hypoadrenocorticism). The condition is sometimes associated with a similar immune attack against other endocrine glands, in particular the thyroid. |
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Keratitis sicca occurs in dogs, with a genetic predisposition in Cocker Spaniels. It can occur in either a primary form or secondary to chronic use of sulfonamides. It is associated with an immune-mediated destruction of the lacrimal glands and is somewhat analogous to Sjögren’s syndrome of humans, which is caused by disease of the salivary glands and a lack of saliva. Of affected dogs, ≥50% respond favorably to eyedrops that contain cyclosporine, which selectively
inhibits disorders mediated by T lymphocytes. |
