Dibutryl cyclic adenosine monophosphate: effect on radiosensitivity of tumors and normal tissues in mice

The effect of dibutryl cyclic adenosine monophosphate (db-cAMP, 30 mg/kg), injected into mice before irradiation, on the radiation sensitivity of various tissues was investigated. Survival of proliferating hair follicles, small gut stem cells, fibrosarcoma (FSa) micrometastases in the lungs, and two different mammary carcinomas, as assayed by the TCD50 method, were studied. Intraperitoneal injection of db-cAMP before irradiation resulted in higher survival of hair follicles irradiated on the third day after plucking. Stem cells in the small gut showed increased survival if irradiated 4 hours after injection. There was no effect on the survival of FSa micrometastases by preinjection and the TCD50/120 days of the mammary carcinomas was not altered.

Asymbiotic association of Rhizobium with pea epicotyls treated with a plant hormone

Treatment of epicotyls of dark-grown pea (Pisum sativum L.) seedlings with indole-3-acetic acid causes swelling of the tissue. Application of Rhizobium to the cut surface of the swollen tissue results in the development of an "infection". The infection spreads in the cortical cells and proceeds 2-3 mm deep into the stem within 3-4 days. An acetylene reduction assay used for detecting nitrogen-fixation capacity of the infected tissue was negative at 10% [O2]; however, if [O2] was reduced to below 1%, some activity could be detected. Ultrastructural observations indicate that the cytoplasmic contents of the infected cells are destroyed and no membrane structure around the bacteria is formed during this infection. Rhizobium does not appear to have developed any symbiotic relationship with the host. Failure to develop symbiosis appears to result in a parasitic or saprophytic association and the nitrogen fixed under such conditions may not be of any use to the plant.

Focal infection in perspective

In this article some of the theoretical possibilities arising as a result of focal infection are discussed. Rheumatic fever is discussed as an example of a disease in which a number of possible mechanisms may act to produce tissue damage at a target area. The mechanisms examined are direct dissemination of organisms from the focus to the target area, the induction of L-phase bacteria, and toxic damage to target tissue. Host-mediated tissue damage by hypersensitivity or auto-immune mechanisms is considered as well.

In vivo transfer of antitumor activity by peritoneal exudate cells from mice treated with C. parvum

We have investigated whether peritoneal exudate cells (PEC) from C. parvum (CP) treated (C3Hf/Bu mice could transfer in vivo the resistance against a syngeneic fibrosarcoma (FSa). Inhibition of tumour development and prolongation of survival of recipients were observed when CP-activated PEC were admixed with FSa cells before their intraperitoneal (ip) or subcutaneous (sc) injections into normal mice. The antitumour activity increased with the increase of the ratio of effector to target cells. Heat killed CP-PEC were unable to transfer the resistance. Also, pretreatment of recipients with 600 rads whole body irradiation (WBI) substantially reduced the efficacy of CP-PEC. Reconstitution of WBI mice with mixed normal spleen and lymph node cells, or spleen cells alone, or bone marrow cells did not restore the antitumor activity of transferred CP-PEC. In fact, reconstituted mice showed a further reduction of transferred antitumor resistance. CP-PEC activity was also inhibited in sc transfer experiments when normal PEC, spleen cells, T-cells or even fetal fibroblasts were admixed with tumor cells and CP-PEC. Possible reasons for the failure of WBI recipients to be fully protected by transferred CP-PEC are discussed.

Combination of C. parvum and specific immunization against artificial pulmonary metastases in mice

We have studied whether specific immunization administered intraperitoneally can augment the activity of C. parvum (0.25 mg intraperitoneally or intravenously) against intravenously injected cells of a syngeneic fibrosarcoma in C3Hf/Bu mice as expressed by the reduction of pulmonary metastases (nodules, colonies) and/or by the prolongation of the survival of recipients. Combination of specific immunization and C. parvum, applied either before or after IV inoculation of viable tumor cells, was more effective than the single treatments. IV injection of a mixture of heavily irradiated and viable tumor cells gave more tumor nodules in the lungs of normal mice than injection of viable cells alone. The metastasis-enhancing effect of admixed irradiated cells was not found in mice previously treated with C. parvum, and was abolished if the immunostimulant was injected after tumor cells. Generation of lung metastases by IV inoculation of fibrosarcoma cells was reduced in mice already having this tumor in the leg. This concomitant immunity to metastases was increased by treating the recipients with C. parvum, but not with irradiated cells; also, the injection of irradiated cells together with C. parvum did not augment the efficiency of the latter. C. parvum was not as effective in T-cell deprived as in control mice, which suggests that in this system, T-cells are required for optimal anti-tumor activity of this immunostimulant. Specific immunization was not effective in T-cell-deprived mice and did not augment the efficiency of C. parvum.