Increased growth promoting but not mast cell degranulation potential of a covalent dimer of c-Kit ligand.

The native form of soluble c-kit ligand (KL) is a noncovalent dimer. We have isolated a soluble, disulfide-linked dimer of murine KL (KL-CD) by expressing KL in Escherichia coli and refolding the denatured protein under conditions that promote the formation of both noncovalent dimers (KL-NC) and KL-CD. KL-CD exhibits a 10- to 15-fold increase in the ability to stimulate the growth of both the human megakaryocytic cell line MO7e and murine bone marrow-derived mast cells relative to KL-NC. Colony-forming assays of murine bone marrow progenitor cells also reflected this increased potency. However, KL-CD and KL-NC are equally able to prime mast cells for enhanced IgE-dependent degranulation in vitro and activate mast cells in vivo. Improving the growth-promoting activity of KL without changing its mast cell activation potential suggests that KL-CD or a related molecule could be administered in the clinic at doses that stimulate hematopoietic recovery while avoiding significant mast cell activation.

Sexual asphyxiation: an unusual case involving four male adolescents.

A case of sexual asphyxiation is described involving children, adolescent males, homosexuality and two bizarre strangulations. Two adolescent males (ages 13 & 10) initially engaged in homosexual activity in conjunction with sexual asphyxiation. This unusual activity was by chance observed by one of the boy's younger brother and his friend. The younger children (aged 7 & 8) expressed a desire to join in the activity, which they did by letting ligatures be tied around their necks and engaging in anal intercourse to the point of fatal asphyxiation. The case is of interest in the reported way the younger boys discovered the practice (a sexually explicit magazine) and is unusual because of the young ages of the boys involved.

Unintentional suffocation by rebreathing: a death scene and physiologic investigation of a possible cause of sudden infant death.

As part of a 1-year study of sudden unexpected infant deaths in St. Louis, we performed both a specialized death scene investigation and, in selected cases, a physiologic reconstruction of the death scene with a rabbit model. Those cases in which the infant was found face down with nose and mouth covered by bedding were chosen for the physiologic testing; our goal was to assess the potential for lethal rebreathing of expired air. The physiologic studies reconstructed the infants' premortem ventilatory environment by using the head from an infant mannequin positioned on the actual bedding on which an infant had died and a rabbit breathing through the mannequin's nares. The specialized scene investigation was carried out in 31 of 32 deaths from sudden infant death syndrome, diagnosed by the usual methods. Of 31 infants, eight died with their faces downward and covered by bedding, and the bedding was obtained for further study in seven of eight cases. The bedding had low resistance to airflow (6.25 to 22.6 cm H2O/L per second), and caused considerable rebreathing that was lethal to the rabbits in five of seven cases. We conclude that items of bedding in common use are capable of causing lethal rebreathing by prone-sleeping infants whose nose and mouth become covered; suffocation by rebreathing was the probable mechanism of death in a substantial number of these deaths that had been attributed to sudden infant death syndrome.