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Natural cytotoxicity in rats: radiation-induced changes in the early killing of allogeneic cells.

In some strain combinations among inbred rats intravenously injected 51Cr-labeled lymphocytes are rapidly destroyed in substantial numbers by unsensitized allogeneic hosts. This phenomenon has been referred to as natural cytotoxicity (NC) and is characterized by decreased lymph node radioactivity, increased kidney and urine radioactivity, and to a lesser extent increased liver radioactivity in allogeneic hosts, when compared with the distribution of label in syngeneic recipients of the same cell suspension. A single exposure to 800 rad either 1 or 7 days before the injection of 51Cr-labeled lymphocytes effected a reduction in NC as defined by all the above parameters in a strain combination exhibiting high NC. The same dosage of radiation abolished NC in a strain combination exhibiting intermediate leads to low NC. Because NC was not always completely abolished, the phenomenon was held to be partially radiosensitive. An increased accumulation of 51Cr-labeled lymphocytes was seen in the lymph nodes of both syngeneic and allogeneic irradiated hosts when compared with nonirradiated controls, although the increase was greater in allogeneic than in syngeneic hosts. This increased colonization in the lymph nodes of irradiated hosts seemed unlikely to be due to an increase in the available "space' in the lymph nodes following irradiation.

Animals↗

Suppression of contact sensitivity and cell-mediated lympholysis by oral administration of hapten is caused by different mechanisms.

Oral administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS), a water-soluble analog of trinitrochlorobenzene (TNCB), causes suppression of contact sensitivity (CS) to picryl chloride. We wished to determine what effect oral administration of TNBS (10mg), 10-12 days prior to sensitization, caused significant suppression of CS to picryl chloride. However, mice had to be fed at least three times at weekly intervals to cause suppression of the CTL response. CS was inhibited both at the afferent (induction) as well as at the efferent (effector) phase of the response. The unresponsiveness for CS was readily transferrable with cells from spleen, Peyer's patches, and mesenteric lymph node cells from fed mice. In contrast, although the hapten specific CTL response was significantly suppressed in mice fed three times. suppression could not be transferred with any of the aforementioned lymphoid populations. Furthermore, spleen cells from fed mice showed a significantly enhanced in vitro CTL response after stimulation with hapten-modified syngeneic stimulator cells. The results indicate that suppression of CS and of the CTL response in TNBS fed mice is probably caused by different mechanisms.

Administration, Oral↗

Role of macrophages as modulators but not as stimulators in primary mixed leukocyte reaction.

The role of macrophages (M phi) and that of splenic dendritic cells (DC) in the allogeneic mixed leukocyte reaction (MLR) in the mouse have been investigated. In contrast with the high stimulatory capacity of DC, we obtained no evidence in favor of the competence of M phi, whether Ia + or Ia-, as an autonomous stimulator of MLR. However, M phi were found to modulate the level of MLR. Thus, M phi amplified the low level MLR to low dose DC and apparently suppressed the high level MLR to high dose DC. Ia + M phi seemed superior to Ia- M phi in the MLR-enhancing effect. M phi syngeneic to the responder and those to the stimulator suggest that M phi are modulators of immune responses triggered through the mediation of DC.

Animals↗