Suppression of the avian reticuloendothelial system and enhancement of a Plasmodium lophurae infection in diethylstilbestrol treated chickens

Melatonin, immunity and cost of reproductive state in male European starlings

The effects of reproductive condition and exogenous melatonin on immune function were investigated in castrated European starlings, Sturnus vulgaris. Photorefractory and photostimulated starlings exposed to long days were implanted with melatonin or with blank capsules. Photostimulated starlings with blank capsules exhibited reduced splenocyte proliferation in response to the T-cell mitogen, concanavalin A, compared with the other long-day birds. Exogenous melatonin prevented the suppression of immune function by photostimulation. Photorefractory starlings, with or without melatonin implants, exhibited enhanced immune function compared with photostimulated starlings implanted with blanks. This enhancement was not mediated by endogenous melatonin, but appeared to be related to changes in reproductive state. In addition to the traditional costs of reproduction in birds (e.g. raising of young), there may be a cost of the reproductive state of starlings (i.e. whether they are photorefractory or photostimulated). These data are, we believe, the first to indicate a direct effect of reproductive state on immune function that is independent of both photoperiod (i.e., changes in the duration of melatonin secretion) and gonadal steroids.

Interrelation of the avian immune and neuroendocrine systems

Our understanding of immunology and endocrinology has been enriched by studies with different avian species. Numerous experiments have identified the role of the avian thymus and bursa of Fabricius in the immune response and the interrelation of these glands and their cellular products with the neural endocrine system. The growth pattern of the thymus and bursa are influenced by steroids. Increases in thymi growth appear to be controlled, in part, by fluctuations in thyroid activity. Sex-linked dwarf (SLD) chicks have lower T3 levels than normal chicks, but normal levels of growth hormone. The poor agglutinin response of SLD chickens to low concentrations of sheep red blood cells (0.1-1.0%) may be overcome by increasing the percentage of sheep erythrocytes to 5 or injecting growth hormone, which may enhance the conversion of T4 to T3. Castration impaired cell-mediated immunity but surgical removal of the thyroid did not significantly influence the humoral response to sheep erythrocytes or Brucella. Embryonic hypophysectomy reduced the number of B cells in the late embryo. Lesioning the anterior pituitary in 9-day-old chicks markedly reduced several parameters of cell-mediated immunity. In ovo bursectomy at 68 hr markedly increased the size of the adrenals and testes, numbers of Leydig cells, and levels of circulating testosterone but not corticosterone. On the basis of identification of lymphokines or cytoplasmic granules, lymphocytes and other cells of the lymphomyeloid complex are candidates for an endocrine role. A circuitry between the lymphocyte and neuroendocrine system has been identified in mammals and should be extended to Aves.

Altered host resistance to Trichinella spiralis infection following subchronic exposure to diethylstilbestrol

The effects of subchronic exposure to diethylstilbestrol on the host response to infection with Trichinella spiralis were examined in adult B6C3F1 mice. Expulsion of adult Trichinella from the small bowel, intestinal inflammation and delayed hypersensitivity responses to Trichinella antigens in artificially sensitized mice were investigated. Administration of 8 micrograms/g of diethylstilbestrol for five consecutive days beginning on days -5,0, +3 or +8 of infection inhibited adult worm expulsion and tissue reactions in the small intestine. Expulsion of adult parasites was also delayed in mice given 0.2 microgram/g of diethylstilbestrol for the first five days of infection. When the chemical was given during a primary infection, mice failed to expel a second infection as rapidly as untreated controls or previously infected mice exposed during a second infection. These findings indicate that diethylstilbestrol exposure altered the immune responses that mediate expulsion of adult worms from the gut, especially when exposure occurred during the inductive phase of host immunity. These results also suggest that use of diethyl-stilbestrol as a weight-gain promoter may lead to increased parasite burdens. While diethylstilbestrol-exposed mice retained adult worms longer than controls, no significant increase was found in numbers of encysted muscle-phase larvae, contrary to the usual findings in animals maintaining adult worm burdens for extended periods. The possibility that macrophages activated by diethylstilbestrol treatment had a role in limiting larvae encystment in the host musculature is discussed.