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The cytotoxicity of radiolabelled YAC-1 target cells by natural killer (NK) cells from the spleens of immunocompetent CBA mice is inhibited by unlabelled YAC-1 competitor cells, but not by resting bone marrow from syngeneic or allogeneic adult mice. Rapidly proliferating haemopoietic cells recovered from the spleens of lethally irradiated, bone marrow-reconstituted CBA mice, however, compete strongly in the NK assay. The competitive ability of early regenerating marrow correlates with the presence of an increased percentage of morphologically immature cells of mixed lineages. Competition declines in reconstituted spleens recovered more than 10 days after engraftment, as the proportion of immature elements falls towards that of resting marrow. Although the numbers of unlabelled YAC-1 cells required to produce equivalent competition of unstimulated and interferon-activated NK killing are similar, 10 times fewer regenerating marrow competitors compete cytotoxicity by unstimulated NK effectors to the same degree as interferon activated cells. The numbers of granulocyte-macrophage colonies formed in soft agar by regenerating marrow is also influenced by prior incubation of the marrow cells with NK effector populations. Spleen cells from homozygous athymic mice produce the same effect as cells from their heterozygous littermates. These data suggest that NK cells recognize and regulate the differentiation of progenitor elements within the marrow.

Natural cytotoxicity (NK) by fresh E-rosette-negative (ER-) cells from normal donors was increased after overnight incubation with purified IFN alpha and with supernatants containing IFN gamma. ER- cells from 61% of 23 patients with systemic lupus erythematosus did not show increased cytotoxicity after treatment with IFN alpha. Similarly, ER- cells from nine of 18 patients that were treated with IFN gamma-containing supernatants failed to show increased cytotoxicity. The patients who did not show enhanced cytotoxic responses to IFN had higher mean indices of disease activity than responding patients.

Twenty-one cases of mediastinal tumors of thymic origin are presented. Five of these were benign and 16 malignant. Surgical excision is proposed as the treatment of choice for the encapsulated benign tumors or for malignant tumors of limited extent. When surgical excision is not feasible, adequate roentgen therapy amounting to 5,000 to 6,000 r calculated tumor dose may eradicate or control the tumor. No correlation between the histological pattern of the tumor and the survival rate or radiation response could be demonstrated in this small series.

A shortened esophagus is probably acquired, rather than congenital, in the great majority of cases. The process by which the shortening develops, as described by Allison and his coworkers, begins with esophageal hiatal hernia, followed by esophagitis caused by the irritation of acids from the stomach, then recurrent ulceration and healing which forms scar tissue which little by little shortens the esophagus. Obesity and relaxation of the supporting musculotendinous structures which accompany advancing years probably are contributory factors in production of esophageal hiatal hernia. Fifteen of a series of 18 patients noted the onset of symptoms on or after the age of 45. Roentgen examination of the esophagus and stomach is indispensable in establishing a diagnosis of acquired short esophagus. Esophagoscopic examination is even more important. In some cases endoscopic differentiation between acute inflammation and carcinoma is difficult. In such circumstances examination of a biopsy specimen taken from the gastric mucosa immediately distal to the area of inflammation or stricture may be helpful. Results in eight patients with advanced esophageal shortening and stricture who were treated conservatively indicate that this should be tried before surgical treatment is considered. For patients with esophageal hiatal hernia accompanied by shortening of the esophagus that is just beginning to produce symptoms, early repair is indicated, since the condition is progressive and the surgical problem is much simpler in the early stages.