Page 299 - Veterinary Immunology, 10th Edition

VetBooks.ir Histiocytosis and Histiocytomas

Domestic animals suffer from several diseases in which
macrophage or DCs proliferate excessively. These are called

histiocytomas or histiocytosis. The most common of these, canine
cutaneous histiocytoma is a benign epidermal neoplasm of
Langerhans cell origin that usually regresses spontaneously.
However, it may metastasize in some dogs. Langerhans cell
histiocytosis is a nonneoplastic reactive lesion whose trigger is

unknown but may be an infectious agent. This condition is not
premalignant, and it may occur in cutaneous or systemic forms.
Both forms of Langerhans cell histiocytosis present as a lesion or

lesions in the skin or subcutis, but systemic histiocytosis also
involves other tissues. Cutaneous histiocytosis shows no breed
predilection, occurs in adult dogs between 3 and 9 years old, and is
characterized by the development of nonpainful solitary or multiple
nodules in the skin or subcutis. These lesions tend to occur on the

head, neck, extremities, perineum, and scrotum. In contrast,
systemic histiocytosis tends to occur in large breeds such as Bernese
Mountain dogs, Rottweilers, Golden Retrievers, and Labradors. The

age of onset is between 4 and 7 years. The lesions develop in the
skin, mucous membranes, eyes, nasal cavity, spleen, lung, liver,
bone marrow, and spinal cord. Histologically these lesions contain
a mixture of cells. The cells express CD1, CD11c, MHC class II, CD4,
and CD90, a phenotype typical of Langerhans cells. The lesions also

contain T cells and neutrophils and may be successfully treated
with corticosteroids, cyclosporine, or leflunomide (Chapter 41). As
many as 30% of cutaneous cases and 10% of systemic cases
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spontaneously regress following infiltration by CD4 T cells and the
production of Th1 cytokines such as IL-2, TNF-α, and IFN-γ, as well
as NOS2, and subsequent recruitment of antitumor effector cells.
Feline progressive histiocytosis is a skin disease presenting as
solitary or multiple nonpruritic nodules on the feet, legs, and face.

These histiocytes express CD1a, CD1c, CD18, and MHC class II
molecules. About 10% of cases express E-cadherin, a characteristic
of Langerhans cells. This is a slowly progressive disease that may

involve internal organs in terminal cases.

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