Mucosal immunity

Sudden infant death syndrome Part 2: the response of the reticuloendothelial system to hypoxemia and infection

The incidence of ascites in chicks raised in a high-altitude chamber doubled from 6500 feet to 8000 feet. A similar condition developed in calves transported to pasture at high altitude. Chicks raised in a high-altitude chamber (compared to controls) produced more plasma cells in the germinal centres of the spleen about four days after an antigen challenge. Children usually suffering from a mild respiratory infection at sea level often developed pulmonary edema (HAPE) on transfer to high altitude. Sudden infant death syndrome (SIDS) victims produced more plasma cells in the germinal centers of the spleen. In one survey of SIDS, about half of the infants suffered an upper respiratory tract infection in the two weeks prior to death and the lungs were filled with fluid at autopsy. Elevated levels of hypoxanthine indicated hypoxemia before death, and a presumed response to hypoxemia in SIDS was the presence of extramedullary hematopoiesis in the liver. The effect of prolonged hypoxemia and infection are additive in increasing vascular permeability and the accumulation of edema fluid. The preferential uptake of zinc by edema fluid proteins at the expense of inflammatory cells increases the motility and metabolism of zinc-deprived activated macrophages. Activated macrophages release cytokines which in turn stimulate the release of pro-inflammatory peptides which increase vascular permeability and mortality. These inflammatory peptides are under proteolytic control. The neutral endopeptidase (NEP) is a cell-surface zinc metalloproteinase which modulates toxic shock.Zinc also modulates the inflammatory response of the activated macrophage. Interleukin-12 (IL-12), predominantly a product of macrophages, is involved in regulating both hematopoiesis and the adaptive immune response. IL-12 promotes interferon gamma (IFNgamma) production by T cells. IFNgamma acts on macrophages to release large amounts of nitric oxide (NO). An elevated immune response leads to NO overload, dilation of the cardiovascular system and toxic shock. A mechanism resulting in cardiovascular failure and a shock-like sequence is described in some cases of SIDS.Bradycardia, recorded on cardiorespiratory monitors in six SIDS infants, was considered a late event. Cytokines regulate all aspects of the immune response. Extramedullary hematopoiesis in the liver was one anatomical marker of hypoxemia in SIDS. This survey traces the function of the activated macrophage with the cytokines regulating extramedullary hematopoiesis and the precocious immune response in SIDS.

Sudden infant death syndrome and superoxide/nitric oxide

In a sudden infant death syndrome review Valdès-Dapena describes Naeye's report of increased medial muscle mass in walls of small pulmonary arteries and increased weight of cardiac right ventricles. These findings point to cardiorespiratory insufficiency, a problem in fast growing chicks raised at high altitudes. The vascular epithelium lining all blood vessels synthesises nitric oxide which induces relaxation of smooth muscle in vessel walls, and is possibly an important neurotransmitter. Others demonstrate that nitric oxide is involved in regulating vessel calibre, blood pressure and blood flow, as well as falls in ventricular outputs. Superoxide interacts with nitric oxide and removes it from the circulation. Superoxide is thus a vasoconstrictor. Superoxide is produced by activated phagocytes and possibly lymphocytes and other cell types in the immune response. Elevated immunoglobulins in mucus secretions are a hallmark in sudden infant death syndrome and hypoxic chicks. Our approach therefore is that cardiorespiratory insufficiency may be induced by superoxide in small pulmonary arteries preventing nitric oxide from acting as a muscle relaxant in vascular walls.

Clinical hypersensitivity to specific aerosol challenge in parenterally immunized calves

This paper reports an experiment designed to demonstrate that the calf lung can be sensitized to a specific respirable challenge following parenteral immunization with a nonliving antigen (human serum albumin). The possibility that immune-mediated injury could subsequently interfere with nonspecific mucosal defenses was also investigated by infecting calves with Pasteurella haemolytica after the antigen challenge and assessing pulmonary clearance of the organism. The results indicated that specific aerosol challenge produces reversible signs of respiratory hypersensitivity and that persistence of incidental infection in the upper respiratory tract is potentiated. Since the calves were sensitized by an immunization regime which imitated conventional vaccination, this study highlights the potential dangers of inactivated parenteral respiratory vaccines.