Page 695 - Veterinary Immunology, 10th Edition

Many cells may be washed out of the airways of the lung with
VetBooks.ir saline. In normal dogs, about 80% of bronchoalveolar cells obtained

in this way are macrophages, and 13% are lymphocytes, of which
about half are T cells (Table 22.1). In healthy horses, about 50% of

the cells in bronchoalveolar washes are macrophages, 40% are
lymphocytes, and 2% are neutrophils. In sheep, B cells are less than
10% of the lung lymphocyte population. Lung T cells can produce
cytokines, and alveolar macrophages are activated following

infection with Listeria monocytogenes. Cell-mediated immune
reactions are therefore readily provoked among the cells within the
lower respiratory tract.

TABLE 22.1

Composition of Cells in Canine Bronchoalveolar Lavage Fluid

Cell Percentage (Range)
Macrophages 79.4 (71-87)
Lymphocytes 13.5 (7-20)
Eosinophils 3.6 (0-14)
Mast cells 2.1 (0-5)
Epithelial cells 0.8 (0-6)
Neutrophils 0.6 (0-2)
Lymphocyte Percentages
T cells 52.0 (34-69)
CD4 + 21.9 (10-32)
CD8 + 17.8 (6-25)
CD4/CD8 ratio 1.3 (0.8-2.4)
From Vail DM, Mahler PA, Soergel SA: Differential cell analysis and phenotypic subtyping
of lymphocytes in bronchoalveolar lavage fluid from clinically normal dogs, Am J Vet Res
56:282-285, 1995.

Alveolar macrophages reside on alveolar surfaces where they are
in direct contact with the air. When they respond to invaders it is
essential that they do not interfere with gas exchange. Thus a full-

scale inflammatory response is to be avoided whenever possible.
For this reason, in the absence of infection, alveolar macrophages
are quiescent and tend to suppress local cytokine production. They
are, however, highly phagocytic. They are also the major producers
of type I interferons that in turn induce inflammation.

The lungs of most domestic species (pigs, horses, sheep, goats,
cattle, cats) differ from rodent, human, or dog lungs in that they
contain large numbers of intravascular macrophages (Chapter 6). It

has been estimated that these macrophages cover 16% of the lung
capillary surface in young pigs. As a result, the lungs of these

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