Page 1470 - Veterinary Immunology, 10th Edition

sinusoids. As a result, they filter blood rather than lymph.
VetBooks.ir Lymphoid aggregates do not seem to be present in the intestine of

urodeles but are seen in anurans.
Larval anurans such as the bullfrog tadpole have lymphomyeloid

organs in their branchial region called ventral cavity bodies.
Sinusoids in these organs are lined with macrophages that
effectively remove particulate antigens from the blood. Removal of
these organs renders tadpoles incapable of making antibodies to

soluble antigens. They disappear at metamorphosis. During
metamorphosis from larval stage to adult, there is a temporary
immunosuppression as shown by slowing of allograft rejection.
Some allografts may even be tolerated at this time. As tadpoles

change into frogs or toads, the thymus shrinks, and there is a drop
in the numbers of B cells and antibody levels (Box 43.3).

Box 43.3

Chytridiomycosis

The massive recent decline in global amphibian numbers is in large
part the result of chytridiomycosis, a disease caused by the fungus
Batrachochytrium dendrobatidis. More than 250 amphibian species

are susceptible to this chytrid fungus found on all the temperate
continents. It affects adult amphibians by causing hyperplasia of
skin keratinocytes. The resulting increase in skin thickness
probably affects osmoregulation and ion balance across the skin.
Frog mortality can reach 100% in some systems and have little

effect in others. In tadpoles, it causes loss of keratinized
mouthparts and hence reduces food intake and survival. It appears
that amphibians have difficulty in clearing this infection. B.

dendrobatidis cells and its culture supernatants impair lymphocyte
proliferation and induce their apoptosis, although fungal
recognition and phagocytosis by macrophages and neutrophils are
not affected. The suppressive factor(s) is present in the fungal cell
wall. The occurrence of this immunosuppression may explain in

part why this organism has had such a devastating effect.

Fites JS, et al. The invasive Chytrid fungus of amphibians paralyzes lymphocyte responses,
Science 342:366-369, 2013.

1470