Radiation sensitivity and cycling status of mouse bone marrow prothymocytes and day 8 colony forming units spleen (CFUs)

Mouse bone marrow prothymocytes as determined in an in vivo thymus regeneration assay have an in vitro gamma radiation sensitivity which is different from that of spleen colony forming cells (CFUs). Determination of Do according to in vivo irradiation revealed similar but insignificant differences. Prothymocytes in normal bone marrow maintain a low but slightly different proliferative state as compared to CFUs, according to determinations using the 3H-TdR suicide technique. In regenerating bone marrow prothymocytes were found to be sensitive to an inhibitory effect of in vitro incubation with cold thymidine. CFUs and normal bone marrow prothymocytes were not affected by cold thymidine. Taking into account the cold thymidine effect it can be concluded that prothymocytes and CFUs in regenerating bone marrow are fully in cycle. These results are best explained when prothymocytes and CFUs are considered to be different cells.     

Immunologic Identification of Tissue Factor (Thromboplastin) Synthesized by Cultured Fibroblasts

The proliferative capacity of bone marrowcells from thymus-deprived nude mice wasinvestigated in lethally irradiated recipients. Although the colony-forming capacityof these cells was found to be similar tothat of normal littermates, a reduction inthe number of nucleated cells was observed in the bone marrow of nude mice.Moreover when the radioprotective effectof such cells was studied, it was foundthat 5 x 10⁵ or 2 x 10⁶ bone marrowcells from nude mice were less effectivein restoring hemopoiesis and establishingpermanent chimerism than similaramounts of bone marrow cells of normalcontrols. In addition, irradiated animalssurviving after injection of bone marrowcells from nude mice were found to havelower immune responses to SRBC thannormal chimeras. The possibility that mortality of irradiated recipients injected withbone marrow of nude mice is due to thepresence of a latent infective agent or ofsome inhibitory factor of hematopoiesis inthe bone marrow of such nude mice isshown to be improbable. Alternatively it issuggested that nude mice suffer from anintrinsic defect in the proliferative capacityof their bone marrow colony-forming cells(CFUs).

Submitted on February 12, 1973 Revised on March 29, 1973 Accepted on April 20, 1973     

The effect of the amount of isologous bone marrow injected on the recovery of hematopoietic organs,survival and body weight after lethal irradiation injury in mice

The relation between the amount of isologous bone marrow injected into alethally irradiated mouse and its 30 day survival, its bone marrow response, thehistology of the bone marrow in its left femur, its peripheral blood leukocytecount, the weight of its thymus, spleen, and body, and its appearance showedthat quicker recovery of these end points occurred with increasing amounts ofbone marrow administered.

The bone marrow parameter was the quickest to respond to the varyingamounts of bone marrow injected. In addition, no optimum dose of bone marrowwas found in these experiments for this end point. This indicates that the bonemarrow of an irradiated mouse could be made to show even quicker return tonormal by injection of greater amounts of cells.

The peripheral blood leukocyte count and the spleen weight also showed veryquick recovery with the massive doses of bone marrow injected. For both endpoints, however, an optimum response was reached, which in the leukocytes, was64.4 x 10⁶ -237.9 x 10⁶ cells injected, and in the spleen weight, 12.8 x 10⁶-237.9 x 10⁶. An optimum response for thymus weight was also found with bonemarrow doses of 64.4 x 10⁶ - 237.9 x 10⁶ cells. The cell dose for the optimumresponse in recovery of body weight was 12.8 x 10⁶ - 237.9 x 10⁶.

Optimum 30 day survival was reached with injection of 64.4 x 10⁶ bone marrow cells in these experiments. However, doses from 12.8 x 10⁶ to 64.4 x 10⁶ cellswere not tested. The dose of bone marrow cells that was calculated to give 50 percent 30-day survival was 0.42 x 10⁶ (0.17 x 10⁶, 1.92 x 10⁶) cells for the malesand 1.06 x 10⁶ (0.42 x 10⁶, 2.51 x 10⁶) cells for the females. The calculated doseof bone marrow cells that would give 1 per cent 30-day survival of the males was0.008 x 10⁶ (0.0008 x 10⁶, 0.0284 x 10⁶) and for the females 0.0102 x 10⁶(0.001 x 10⁶, 0.040 x 10⁶) cells. These point estimates seem to be unreliable inview of the extremely large 95% confidence intervals. However, in experimentsdone by other workers at the National Cancer Institute similar to those reportedin this paper, M. Schneiderman determined a threshold dose ranging from 0.0026to 0.0320 x 10⁶ cells by a somewhat different analysis of the data.⁷ Jacobson et al.cite a figure of 3-5 x 10⁶ bone marrow cells from young donor mice as causing53% 28-day survival in CF No. 1 mice exposed to 900 r.² In using bone marrowfrom older mice, they found that 5-9.9 x 10⁶ cells caused 54.9% 28-day survival.They also estimate that 50,000 cells are necessary to produce significant recoveryof mice after an LD₉₉ exposure. This figure is similar to that determined from theresults of the present experiments.

The results obtained from mice injected intravenously with a massive dose ofbone marrow 3 days after irradiation indicated that the number of cells in thebone marrow of the right femur can be elevated within a few hours after injection.However, this could be observed only in an irradiated animal where the numberof cells in the right femoral bone marrow was already low. A similar observationwas made by Graevsky.⁸ This finding gives further support to the hypothesisthat intravenously injected bone marrow transplants to bone marrow sites in theirradiated host.⁹

Submitted on July 9, 1956 Accepted on August 12, 1956     

The Metabolism of Transferrin-bound 111In and 59Fe in the Rat

The metabolism of transferrin-bound indium and iron were compared by in vivostudies in the rat. Rats were injected withserum transferrin labeled with ¹¹¹In and⁵⁹Fe, and, at intervals ranging from 20min to 5 days after injection, they werekilled. They were perfused through theportal vein with 200 ml of 0.9% saline,and the residual radioactivity, expressedas a percentage of the injected dose, wasmeasured in liver, spleen, kidney, muscle,washed red cells, red marrow, and femur.At 5 days, 76% of the injected ⁵⁹Fe wasrecovered in the red cell mass; only1%-2% of ¹¹¹In could then be recovered.Uptake and release of the ¹¹¹In label bythe femur was markedly less than that ofthe ⁵⁹Fe. Whereas 85% of the injected⁵⁹Fe could be recovered from the circulating red cells, liver, and spleen, only about15% of the injected ¹¹¹In could be so recovered. Approximately 35% of the injected ¹¹¹In was excreted, and 43% wasrecoverable from the carcass. The subcellular distribution of the two isotopes in theliver at timed intervals following intravenous injection was studied. While 35%of the ⁵⁹Fe activity in the homogenatewas associated with ferritin, only 4% ofthe ¹¹¹In could be so identified. The results indicate a significant difference between the metabolism of ¹¹¹In and ⁵⁹Fein the rat and make it unlikely that themetabolism of ^In in man bears muchsimilarity to that of iron.

Submitted on October 2, 1973 Revised on October 28, 1973 Accepted on October 30, 1973     

Procoagulant activity of lymphocyte-macrophage populations in rabbits: selective increases in marrow, blood, and spleen cells during Shwartzman reactions

The present experiments examine leukocyte procoagulant activity using mononuclear cell populations purified or enriched from rabbit bone marrow, blood, spleen, lymph node, thymus, and pulmonary alveoli. Cells from these six sites, obtained from control and endotoxemic animals and assayed without an intermediate culture step, were found to have procoagulant activity identified as tissue factor. Under control conditions, tissue factor activity was found to be at low levels in marrow and blood populations compared to median activities 3- and 11- fold higher in populations from spleen and lymph node, and 33- and 45- fold higher in thymus and alveolar populations. By contrast to respective controls, significantly increased amounts of tissue factor (35-, 15-, and 12-fold at median levels) were found in marrow, blood, and spleen populations from endotoxemic animals. The types of leukocytes in these latter three populations were morphologically and histochemically indistinguishable from respective controls, indicating that endotoxin induced increases of activity in cells with relatively low amounts under control conditions. Activity did not change significantly in lymph node, thymus, or alveolar populations after endotoxemia. These studies show that tissue factor is present in a range of leukocyte populations not previously reported to have procoagulant activity. In addition, the finding of widespread gains of tissue factor in the marrow-blood-spleen pool due to endotoxemia provides new evidence supporting the importance of leukocyte procoagulants in Shwartzman-like reactions.     

Evidence for structured variation in self-renewal capacity within long-term bone marrow cultures.

Bone marrow pluripotent stem cells (CFUs) demonstrate capacity for both proliferation and differentiation. The proliferative capacity of CFUs has been measured by serial transplantability and by the Rs, a measurement of CFU production in a single 14-day transfer. In the present study, the self-renewal capacity fo both adherent and nonadherent CFUs from long-term bone marrow cultures was measured. Culture conditions were established such that nonadherent cells were derived from the adherent cell layer. Both adherent and non-adherent cells produced spleen colonies, demonstrating that significant proliferative potential was present in both locations; however, at all times in culture, the CFUs within the adherent stromal cell layer had a significantly greater self-renewal capacity than did the nonadherent CFUs. During the initial establishment of the cultures, the self-renewal capacity of the adherent CFUs decreased as the total number of CFUs per flask increased. After 3 weeks in culture, the self-renewal potential of the adherent CFUs stabilized and was maintained. These results suggest two different mechanisms of stem cell proliferation. In order to increase the most primitive stem cell pool size, there was initial proliferation of early stem cells with a concomitant decrease in self renewal capacity. Once this pool was established, the self-renewal capacity of the adherent CFUs maintained for 13 weeks in culture suggests that CFU production and cell maintenance were achieved by clonal succession.     

Comparison of the effectiveness of bone marrow and spleen stem cells for platelet repopulation in lethally irradiated mice

To determine whether stem cells from spleen differ from those of bone marrow in their ability to support platelet repopulation after lethal irradiation we compared normal, splenectomized and plethoric (3 weeks exposure to CO) spleen cell recipients with similar groups of mice reconstituted with comparable numbers of bone marrow stem cells. Female LAF1 mice were given 825-950 R from a 60Co source and were transplanted with 0, 0.5, 1, 2, or 4 x 10(6) bone marrow or 10-64 x 10(6) spleen cells. CFUs content of the transplant was calculated from day 9 splenic nodules in mice receiving 5 x 10(4) bone marrow or 1.0-1.6 x 10(6) spleen cells. Blood volumes, platelet counts and hematocrits were determined on day 12. Total circulating platelets increased with increasing stem cell dose (range 50-1000 CFUs) after both types of transplant. Plethoric mice always had lower platelet levels than controls even when corrected for expanded blood volume. There was little difference between values for normal and splenectomized mice. Platelet production per CFUs in all groups except splenectomized spleen cell recipients declined with large transplants presumably because of feedback inhibition. Although the number of splenic megakaryocytes in spleen cell recipients was approximately 2.5 times as great as in bone marrow recipients, platelet levels were significantly higher only in normal and splenectomized mice receiving more than 300 CFUs. No differences were found between the two types of transplant when plethoric hosts were used.     

Haematopoiesis in Busulphan-Treated Mice: A Comparison between Two Different Stem Cell Assays

The effect of busulphan on haematopoiesis was investigated in mice. Bone marrow and blood cells were sampled 2 h to 55 d after a single treatment with busulphan. The effect on progenitor cells was examined with the diffusion chamber (DC) technique and the spleen colony assay. Busulphan had a severe depressive effect on progenitor cells in bone marrow, and their number was reduced to 0.01–0.1 % of the control value on day 5–6. During the first 2 d the CFUs were reduced more than granulocyte progenitors as determined in the DC system. Histological examination of spleen colonies showed that in the same interval erythroid colony number was more depressed than granuloid colony number. This situation reversed after 4–6 d. Our interpretation is that busulphan affects all types of progenitor cells irrespective of their proliferative state. However, multipotent CFUs in G_o-phase are more depressed than granulocyte progenitor cells (DC), which have a higher proliferative rate. The selective effect on erythroid colonies during the initial period might indicate that busulphan impairs the ability of multipotent CFUs to erythroid differentiation. This damage was repaired within a few days. An abortive regeneration of bone marrow cells was observed on day 7–10. This can best be explained by an inflow from a cell pool intermediate between stem cells and early precursor cells, with some degree of ‘stem-cellness' (self-sustaining capacity).     

Hydroxyurea as a suppressor of the radioprotective effect of dextran sulfate on bone marrow hemopoietic stem cells in mice.

The changes in hemopoiesis of mice following intraperitoneal administration of dextran sulfate (DS) 24 h before irradiation, as well as the effect of injecting them with hydroxyurea (HU), were analyzed. DS increased the proliferation activity and number of hemopoietic stem cells (CFUs) in the bone marrow. The content of CFUs in the bone marrow and the number of endogenous spleen colonies (ESC) of hemopoietic tissue were higher after irradiation in mice treated with DS than in control groups. The survival rate following a lethal radiation dose was also higher. Injection with HU decreased the number of CFUs in animals injected with DS to the level of controls and suppressed its radioprotective effect.     

Parameters of Marrow Proliferative Capacity In Vitro: Detection of a Sex Difference in Normal Human Granulopoiesis

Sixteen bone marrow aspirates from normal males, cultured in vitro at variousconcentrations, were compared with tenaspirates from normal females. Marrowfrom males produced a significantly highercolony count than females when plated ata standard concentration of 2.0 x 10⁵cells per dish. This difference in colony-forming ability was found to be cell-doserelated when dose-response studies foreach marrow were obtained at concentrations of 1.0, 1.5, and 2.0 x 10⁵ cells perplate. To more fully characterize marrowproliferative capacity in vitro, two additional parameters of growth were defined:(1) the slope of the dose-response curveand (2) the extrapolated cell concentrationat "zero" colony growth. These parameters were found to differ significantlybetween male and female marrows andsuggest that the mechanism of steady-state regulation of resting marrow maydiffer in males and females.

Submitted on July 17, 1973 Revised on December 5, 1973 Accepted on December 9, 1973     

Proliferation of Haemopoietic Stem Cells in Vitro

S ummary . A liquid culture system for murine haemopoietic cells is described where proliferation of granulocytes (G-cultures) or mononuclear cells (M-cultures) can be maintained for many weeks. In M-cultures there is a rapid loss of spleen colony forming cells (CFUs). Agar colony forming cells (CFUc) are present for 6 weeks, then decline rapidly. Colonies formed from these CFUc contain only large mononuclear cells. In G-cultures there is proliferation of CFUs, grafts of which (after 7-9 weeks in culture) protect lethally irradiated mice from haemopoietic death. Similarly, there is proliferation of CFUc, which form colonies in agar consisting of granulocytes, in all stages of differentiation.     

Some Properties of the Circulating Hemopoietic Stem Cells

Some properties of hemopoietic stem cells(CFU) circulating in the peripheral blood ofthe normal mouse (PCFU) were studied.Those parameters were chosen that arewell-known characteristics of bone marrow stem cell populations. Leukocytesseparated from the peripheral blood werethe source of PCFU. The radiosensitivity(D₀ value), growth curve, seeding efficiency (f number), and the turnover state(number of PCFU in S phase measured by³H-thymidine killing technique in vitro) ofPCFU were compared to the same parameters for bone marrow CFU. Several characteristic changes in these parameterswere found for PCFU: (1) Lower radiosensitivity (D₀ = 140 R), (2) Higher seedingefficiency (f number 20.9%), (3) Highersensitivity to ³H-thymidine in vitro (killingeffect 32%). The doubling time was thesame both for CFU and PCFU (21 hr), butthe logarithmic growth of the PCFU population started by approximately 36 hr laterthan that of the marrow-derived CFU population. All these findings support the ideathat PCFU represent a subpopulation ofthe heterogeneous bone marrow CFUpopulation.

Submitted on May 16, 1973 Revised on September 18, 1973 Accepted on October 18, 1973     

Selective Toxicity of Diphtheria Toxin for Malignant Cells

Purified diphtheria toxin is shown to inhibit protein synthesis in Ehrlich-Lettré ascites carcinoma cells in vitro. Protein synthesis in Ehrlich-Lettré cells is at least 10,000 times more sensitive to toxin than protein synthesis in normal mouse spleen or thymus cells. This sensitivity correlates with the observation that Ehrlich-Lettré tumors regress in mice injected with diphtheria toxin but not diphtheria toxoid. Using the criterion of inhibition of protein synthesis in vitro, we show that other mouse malignancies (lymphoma and myeloma) are also more sensitive to diphtheria toxin than normal spleen or thymus. Metastatic human breast carcinoma cells from two individuals, cells from two melanoma nodules removed at different times from a third patient, and cells from melanoma nodules from three additional individuals are shown to be more sensitive to diphtheria toxin than some normal human cells. The toxin sensitivity of protein synthesis in some of the malignant cells tested was so much greater than that of normal cells, that we have proposed that diphtheria toxin should be studied further since it might prove a useful anti-cancer agent in patients whose tumors are first shown to be highly sensitive to toxin in vitro.     

Factor XIII Deficiency: A Genetic Study of Two Affected Kindreds in Finland

Factor XIII deficiency is a congenital defectof the blood coagulation system. Activatedfactor XIII is the fibrin cross-linking enzyme that catalyzes the formation of N⁶--glutamyllysyl bonds in fibrin. Congenital deficiency of factor XIII has beendescribed in approximately 65 separatefamilies. It is apparent that this is ahereditary trait, but the mode of inheritance is unclear. In this study two unrelated Finnish families with factor XIIIdeficiency were investigated in order todetermine the pattern of inheritance. Onefamily had only affected male members,and in the other both males and femaleswere affected. Plasma factor XIII levelswere measured by the fluorescent amineincorporation assay, which has been foundto be sensitive to the detection of heterozygotes. In both families it was found thatthe parents of the affected children wereindeed heterozygous for factor XIII, and asfar as could be determined in the pedigrees each heterozygote had at least oneheterozygous parent. This study indicatesthat in these two families the mechanismof inheritance of factor XIII deficiency isautosomal recessive. Comparison of thesefamilies with others reported in the literature suggests that an autosomal recessivepattern is the general mode of inheritancein factor XIII deficiency.

Submitted on July 31, 1973 Revised on August 25, 1973 Accepted on August 27, 1973     

In Vitro Growth of Granulocytic Colonies From Circulating Cells in Human Cord Blood

Human umbilical cord blood cells from 26newborn infants and peripheral blood cellsfrom 18 adults were cultured in vitro byusing the agar-gel method of humanhemopoietic cell culture. An increasedconcentration of colony-forming cells wasseen in the cord blood cultures. Between17 and 385 colonies, with a mean of 122,were formed in these cultures per 2 x10⁵ nucleated cells plated. The peripheralblood cell cultures from adults gave rise to0-11 colonies, with a mean of 3, per 2 x10⁵ nucleated cells plated. The averagenumber of cells per colony was 1000-1500cells after 14 days of culture, predominantly granulocytic.

Submitted on April 10, 1973 Revised on August 27, 1973 Accepted on August 29, 1973     

The Effect of Syngeneic Peripheral Blood Cells on the Formation of Colonies by Normal Human Bone Marrow Cells in Diffusion Chambers in Mice

This paper describes the influence of cells capable of releasing colony stimulating activity (CSA) in vitro on the formation of granulocytic colonies by normal human bone marrow in diffusion chambers in mice. A carbonyl iron method was used to remove phagocytic cells from normal human bone marrow. This treatment prevented spontaneous colony and cluster formation when the cells were cultured in agar in vitro at initial concentrations of 2–5 times 10⁵cells per ml. However, non-phagocytic bone marrow cells formed granulocytic colonies when inoculated into diffusion chambers at 10⁵cells per chamber and cultured in 450 R-irradiated or non-irradiated mice. The formation of granulocytic colonies by carbonyl iron treated marrow in diffusion chamber cultures was not consistently enhanced by the admixture of 1.4 times 10⁵1500 R-irradiated syngeneic light density blood cells (< 1.077 g/ml) to the chamber inoculum. In contrast, these cells induced cluster or colony formation when added in the same proportion to the marrow cells in agar cultures in vitro. Addition of 1.4 times 10⁵1500 R-irradiated high density blood cells (> 1.077 g/ml) to the inoculum resulted in a slight, non-significant decrease in the number of colonies in diffusion chambers. The stimulating effect of host irradiation on neutrophilic colony formation was independent of the presence of CSA releasing cells in the chamber inoculum.     

Cytochemical and Radioautographic Identification of Cells Induced to Synthesize Hemoglobin

In order to facilitate the identification ofbone marrow cells in which hemoglobinsynthesis is initiated, erythropoiesis wasfirst suppressed in guinea pigs through theinduction of posthypoxic polycythemia,and then it was restimulated by bleedingand reexposure to hypoxia. Hemoglobinsynthesis was detected with ⁵⁵Fe incorporation on radioautographs, and itspresence was demonstrated in the lightmicroscope with the benzidine reactionand absorption of monochromatic light at 4046 Å. In the electron microscope,hemoglobin was detected in the cytoplasm by a general increase in electrondensity after treating the tissue withdiaminobenzidine (DAB) and OsO₄. Densitometric measurements were carried outon electronmicroscopic negatives, usingreticular cell cytoplasm as a base line. Innormal marrow, proerythroblasts were theearliest cells in which hemoglobin couldbe detected, but during the early phase oferythropoietic stimulation, hemoglobinwas demonstrated in transitional cellswith all the methods employed. Withoutthe specific demonstration of hemoglobin,these cells could not be recognized morphologically as erythroblasts nor couldthey be distinguished from the precursorsof bone marrow small lymphocytes.Transitional cells were numerous in themarrow at the time of stimulation, and40 hr later a small number of them werelabeled with ⁵⁵Fe and synthesized hemoglobin in detectable amounts. Proerythroblasts were absent at the time of the stimulus, and when they reappeared themajority were benzidine or DAB positiveand had incorporated ⁵⁵Fe. The findingssuggest that progenitor cells of erythroblasts are among the basophilic membersof the transitional cell population, anderythropoietic stimulation induces hemoglobin synthesis in them. The relationshipof these cells to the progenitors of otherhemopoietic cells, as well as to the pluripotent stem cell, is discussed.

Submitted on May 29, 1973 Revised on November 12, 1973 Accepted on November 15, 1973     

On the Origin of Foà-Kurloff Cells

The thymic and splenic release of Foà-Kurloff cells into the blood was studied in estradiol-treated male guinea pigs by comparison between the cellular content in afferent and efferent blood. The amount and distribution of such cells in thymus, spleen, lymph nodes, and bone marrow was investigated. The treatment with estradiol caused involution of the thymus and splenomegaly. An abundance of Foà-Kurloff cells was found in the red splenic pulp and a considerable release of such cells from the spleen into the blood was demonstrated. At the same time the output of lymphocytes from the spleen was reduced, suggesting that the Foà-Kurloff cells are transformed lymphocytes. The spleen contained an increased amount of erythroblasts, indicating a stimulation of splenic erythropoiesis by estradiol. In the bone marrow and the thymus the number of Foà-Kurloff cells was much smaller than in the spleen and no emigration of such cells from the thymus into the blood was demonstrated. A very small amount of Foà-Kurloff cells was found in the lymph nodes and very few occurred in the thoracic duct lymph. Thus, the Foà-Kurloff cells of the blood do not originate in the lymph nodes and do not recirculate between blood and lymph. It is concluded that the spleen is the major producer of Foà-Kurloff cells and that they are released from the spleen into the blood.     

Abnormalities in myelopoietic regulatory interactions with acidic isoferritins and lactoferrin in mice infected with Friend virus complex: association with altered expression of Ia antigens on effector and responding cells

The regulation of myelopoiesis was evaluated in B6D2F1 mice inoculated with Friend virus complex (spleen focus-forming virus plus helper virus) or helper virus alone by analyzing acidic isoferritin (AIF) and lactoferrin (LF) interactions with target cells. Under normal conditions, AIF suppresses colony and cluster formation by an Ia- antigen-positive cycling subpopulation of mouse granulocyte-macrophage progenitor cells (CFU-GM). Under the same conditions, the release of AIF-inhibitory activity and granulocyte-macrophage colony stimulatory factors (GM-CSF) from an Ia-antigen-positive subpopulation of monocytes and macrophages is suppressed by LF. Within one to two days after inoculation in vivo with Friend virus complex or helper virus, mouse CFU-GM become insensitive in vitro to suppression by purified human AIF as well as crude mouse AIF, and by four days, bone marrow, spleen, and thymus cells of these mice release much greater quantities of AIF- inhibitory activity than the cells from mice injected with control medium. The Friend virus complex itself has no influence in vitro on CFU-GM from normal mice. In addition, the release of AIF-inhibitory activity from bone marrow, spleen, and resident peritoneal cells and the release of GM-CSF from resident peritoneal cells of mice infected with Friend virus complex are not suppressed by LF. The inability of AIF to suppress colony formation by bone marrow and spleen CFU-GM from mice infected with Friend virus complex is associated with the loss of Ia (I-A subregion) antigens from CFU-GM, even though CFU-GM are in cycle. The nonresponsiveness of bone marrow, spleen, and peritoneal cells from these mice to LF suppression of AIF release and the inability of LF to influence GM-CSF release from peritoneal cells is associated with loss of Ia antigens from these cells. The above abnormalities are similar to the defects noted using cells from patients with leukemia. These results suggest that mice infected with Friend virus complex can serve as a model for investigating abnormalities in cell regulation and their relationships to disease progression.     

The Effect of Phytohaemagglutinin on Human Foetal Cells Grown in Culture

Cell suspensions of foetal thymus, liver, spleen and bone marrow have been grown in cell culture and the effect of adding PHA observed. ³H thymidine uptake by the cells after exposure for a measured time was quantitated by autoradiographic counts performed on the initial suspensions and following culture. The initial unstimulated liver and thymic cell suspensions had a high level of ³H thymidine uptake, while that of the spleen and bone marrow cells was low. After 3 days culture the unstimulated cells from the liver, thymus and bone marrow showed very little ³H thymidine uptake, while that of the spleen was slightly increased. Foetal thymic and splenic cells responded to PHA while liver and bone marrow cells did not. The findings suggest that foetal cells of similar morphology may have different origins in the reticulo-endothelial system.