Page 865 - Veterinary Immunology, 10th Edition

VetBooks.ir Adverse Consequences of the

Immune Responses

Although immune responses are beneficial in that they eliminate
invading bacteria, this is not always the case. The immune
responses can influence the course of a bacterial disease without
producing a cure and in some situations may increase its severity.

The adverse consequences of the immune responses correspond in
their mechanisms to the hypersensitivity types described in
Chapters 29 to 33. For example, a local allergic reaction is
sometimes seen in sheep vaccinated against foot rot by means of

Dichelobacter nodosus vaccine, but in this case it is believed that the
hypersensitivity may assist in preventing reinfection.
Type II (cytotoxic) reactions may account for the anemia that
occurs in animals with salmonellosis. In these infections, bacterial

lipopolysaccharides from disrupted bacteria are adsorbed onto
erythrocytes. The subsequent immune response against the
bacterium and its products therefore results in red cell destruction.
Type III (immune-complex) reactions may contribute to the

development of arthritis in Erysipelothrix rhusiopathiae infections in
pigs or to the development of intestinal lesions in Johne's disease
due to MAP. In the former case, bacterial antigen tends to localize
in joints, where local immune-complex formation then results in

inflammation and arthritis. Passively administered antiserum may
therefore exacerbate the arthritis in these infected animals. In
Johne's disease, type I or type III reactions occurring in the
intestinal mucosa may increase the outflow of fluid and diarrhea. It

is clear, however, that the intestinal lesions in this disease are
etiologically complex since diarrhea can be transferred to normal
calves by either plasma or leukocytes, and antihistamine drugs may
reduce the diarrhea. Type III hypersensitivity reactions are

involved in purpura hemorrhagica of horses, in which immune-
complex lesions result from Streptococcus equi infection (Chapter 32).
Although cell-mediated (type IV) immune responses are
manifestly beneficial, they do contribute to the development of

granulomatous lesions in some chronic infections.

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