Life table analysis and pathologic observations in male mice of a long-lived hybrid strain (Af X C57BL/6)F1

We have utilized a long-lived (Af X C57BL/6)F1 hybrid strain of mice for a variety of aging studies. In this report we have characterized the life expectancy and pattern of spontaneous deaths in 202 mice, malignant and nonmalignant lesions in 64 male mice dying spontaneously, and organ weights and lesions in 39 male mice killed at selected ages. The maximum age observed was 41.5 months. The principal causes of death were malignant lymphoma and alveologenic neoplasms, which were present in 56.3% and 45.3%, respectively, of the mice dying spontaneously. A variety of other neoplastic and non-neoplastic lesions that are not infrequently seen in older mice were observed in these mice. Neoplasms seen in these mice that are rare in other mice included disseminated mast cell tumors in two mice and gastric adenocarcinoma in one mouse. In comparing the diseases observed in this hybrid strain with those reported for the parent strains, there was an incidence of malignant lymphoma similar to the C57BL/6 parent, an incidence of alveologenic neoplasms intermediate between the parent strains, and a markedly reduced incidence of amyloidosis. This study provides a detailed background of baseline hematologic and morphologic data in a long-lived hybrid of two commonly used strains of mice.

Kinetics of early and late spleen colony development

The kinetics of spleen colony development were studied with special emphasis upon the self-replicative capacity of CFU-S, which are responsible for the early- or late-appearing spleen colonies, and upon CFU-S migration in the days following transplantation. It was found that, while the spleen colonies had a much lower daughter CFU-S content at eight days than at 11 or 12 days, many of the 8-day colonies remained in the spleen to become 12-day colonies which had many daughter CFU-S. In addition, it was found that large numbers of CFU-S were present in the splenic space between the colonies. Evidence was developed that these "intercolonial space" CFU-S were the founders of many of the late-appearing spleen colonies and that many or all of them were transported from the bone marrow to the spleen via the blood at varying times after the transplantation. Approximately one-half of the day-12 colony founders were found to arrive in the spleen after the third posttransplantation day.

Normal cycling patterns of hematopoietic stem cell subpopulations: an assay using long-term in vivo BrdU infusion

It was found in a long-term bromodeoxyuridine (BrdU) infusion study that two or more different subpopulations of bone marrow stem cells exist in mice. One of these subpopulations appears to be noncycling and forms approximately 10% of eight-day CFU-S. Another one, a subpopulation of slowly cycling bone marrow cells, is represented as 14-day CFU-S. The 14-day CFU-S have a regular increment in the percentage of the subpopulation entering the cycle over time, with a cell generation half-time of 21 days. The cycling status in these experiments was ascertained by in vivo continuous long-term BrdU infusion. An improved method is presented for long-term BrdU infusion with UV killing of cycled cells.

The decline in murine splenic PHA and LPS responsiveness following serial transplantation of young and old bone marrow cells

An analysis was made of the ability of bone marrow cells derived from young (6 months) or old (28 months) murine (A X C57BL/6) donors to differentiate to B and T lymphocytes following serial bone marrow cell transplantations into groups of young syngeneic lethally irradiated recipients. Both number and mitogenic responsiveness of splenic B and T lymphocytes were recorded for recipients of young or old bone marrow cells 9 months following each serial transplant. The data suggests that lymphopoietic stem cells senescence in a manner analogous to that predicted by the clonal succession model of ageing.

A technique for the daily examination of spleen colonies in mice

We have developed a surgical method and an insertable device for viewing the daily changes in number, shape, and development of hemopoietic spleen colonies in mice. With it we have been able to follow the spleen colony changes in individual animals over the period when macroscopic or moderately magnified counts of spleen colonies are customarily made. We have found that about half of the spleen colonies present on day 8 after transplantation do remain through day 12, while an approximately equal number disappear during this period. Further, the colonies that disappear are replaced by an equal or larger number of newly developing colonies at roughly the same temporal sequence as their disappearance. We speculate that these late-appearing colonies may be late arrivals from the recipient's previously seeded bone marrow.

The decline in murine splenic PHA and LPS responsiveness with age is primarily due to an intrinsic mechanism

Changes in splenic B and T lymphocyte number and mitogenic activity with age were quantitated in (A X C57BL/6)F1 (AB6F1) hybrid mice. Although both the B and T lymphocyte proliferative reactivity to their respective mitogens, lipopolysaccharide (LPS) and phytohemagglutinin (PHA), declined significantly with age, an earlier and more marked reduction was recorded for the T cell response. The decline in B and T lymphocyte mitogenic activity with age could not be correlated with a corresponding reduction in the percentage of splenic B or T lymphocytes. The main focus of this study was to determine if the reduction in T and B lymphocyte mitogenic activity with age results primarily from a mechanism intrinsic to the lymphoid lineage itself or from adverse extracellular factors that increase with age. Bone marrow cells (BMC) derived from individual young and old donor AB6F1 mice were transplanted into the neutral environment of young, lethally irradiated syngeneic recipients. Number and mitogenic activity of splenic T and B lymphocytes were recorded for the original BMC donors as well as for the recipients of the young and old BMC lines 9 mo after the BMC transplants. A predominance of the donor (male) rather than recipient (female) karyotype within the mitogen-responding populations of recipient mice confirmed a donor BMC take. The PHA and LPS response levels exhibited by the old donors were 30% and 70% of those of the young donors, respectively. These differences in PHA and LPS reactivity recorded between young and old donors were maintained between recipients of young and old donor BMC lines. Thus, even under the influence of a young recipient environment, old BMC were incapable of giving rise to mitogen responding cells with a functional competence equivalent to that of their younger counterparts. This finding would lend further support to the theory that an intrinsic mechanism is responsible for the decline in murine mitogenic activity with age.

The decline in murine splenic PHA and LPS responsiveness with age is primarily due to an intrinsic mechanism

Changes in splenic B and T lymphocyte number and mitogenic activity with age were quantitated in (A X C57BL/6)F1 (AB6F1) hybrid mice. Although both the B and T lymphocyte proliferative reactivity to their respective mitogens, lipopolysaccharide (LPS) and phytohemagglutinin (PHA), declined significantly with age, an earlier and more marked reduction was recorded for the T cell response. The decline in B and T lymphocyte mitogenic activity with age could not be correlated with a corresponding reduction in the percentage of splenic B or T lymphocytes. The main focus of this study was to determine if the reduction in T and B lymphocyte mitogenic activity with age results primarily from a mechanism intrinsic to the lymphoid lineage itself or from adverse extracellular factors that increase with age. Bone marrow cells (BMC) derived from individual young and old donor AB6F1 mice were transplanted into the neutral environment of young, lethally irradiated syngeneic recipients. Number and mitogenic activity of splenic T and B lymphocytes were recorded for the original BMC donors as well as for the recipients of the young and old BMC lines 9 mo after the BMC transplants. A predominance of the donor (male) rather than recipient (female) karyotype within the mitogen-responding populations of recipient mice confirmed a donor BMC take. The PHA and LPS response levels exhibited by the old donors were 30% and 70% of those of the young donors, respectively. These differences in PHA and LPS reactivity recorded between young and old donors were maintained between recipients of young and old donor BMC lines. Thus, even under the influence of a young recipient environment, old BMC were incapable of giving rise to mitogen responding cells with a functional competence equivalent to that of their younger counterparts. This finding would lend further support to the theory that an intrinsic mechanism is responsible for the decline in murine mitogenic activity with age.

Effect of a neutrophilia-inducing tumor on hemopoietic stem cells in mice

The influence of neutrophilic stimulation on hemopoietic stem cells was studied in mice with tumor-induced neutrophilia. Transfusions of marrow cells from normal and neutrophilic tumor-bearing mice into lethally irradiated normal and tumor-bearing mice were performed. The number and the erythroid:granuloid (E:G) ratio of day 7 colonies in the recipient spleens and bones as well as the size of spleen colonies of recipient animals were determined. The E:G ratio of spleen and bone marrow colonies between normal and tumor-bearing mouse recipients and the number of spleen colonies did not differ significantly in either experiment. However, spleen colonies which developed in tumor-bearing irradiated mice were significantly larger than those which developed in normal recipients in both experiments. These studies indicated that while the line of differentiation taken by hemopoietic stem cells was not affected by the neutrophilic influence of the tumor, the tumor-bearing host environment appeared to enhance proliferation of transfused stem cells and/or their descendants. The stimulators of granulocytopoiesis in this model of neutrophilia appear to act on a population of progenitor cells more mature than the stem cells capable of forming 7-day colonies in the spleen and bone marrow of irradiated recipient mice.

Depletion of reserve in the hemopoietic system: III. Factors affecting the serial transplantation of bone marrow

The effects of serial transplantation on murine bone marrow were studied. Decline of CFUs content and the maximum number of successful transplantations possible were the criteria considered to indicate stem cell changes accompanying the serial transplants. Variables of experimentation included age of the marrow cell donors, addition of thymocytes to the transplanted marrow, differing time intervals between transplantations and differing numbers of donor marrow cells injected throughout a given transplant series. All of the transplantation series were monitored by karyotyping the marrow cells after each transplantation to document the continuance of the original donor cells. Reversions to recipient cell type did occur late in some series and were considered the end point of these series, as were the disappearance of CFUs and deaths of recipients due to transplant failure (the latter two always corresponded well). Only the donor marrow cell dose was found to be an important variable in the continuance of a transplant series and it was possible to obtain 8 successful serial transplantations with the highest marrow cell dose. All of the series given lower cell doses failed at the fifth or sixth transplant, regardless of other variables involved. A naturally occurring hierarchy of hemopoietic stem cells coupled with stem cell differentiative changes caused by extreme and repeated demands for population replenishment is offered as a probable reason for the results obtained, while other possibilities are discussed as well.

Depletion of reserve in the hemopoietic system: I. Self-replication by stromal cells related to chronologic age

Transplanted devascularized mouse femurs and spleens or spleens ligated in situ all undergo a period of massive necrosis followed by a period of cellular regeneration and reconstitution of tissue components. This renewal of stromal tissue is endogenous to the organ and proliferates inward from a thin rim of surviving cells. Components of the femoral or splenic stroma constitute a hemopoietic microenvironment whose functions include the lodgment, commitment to differentiation and support of the proliferation of hemopoietic stem cells and their differentiating descendents. By using measures of the ability to support hemopoiesis, and the histological appearance of the reconstituted hemopoietic organs, it was shown that the degree of regeneration of the stroma was inversely related to its chronological age. Thus, although age-related changes in stromal cells are not readily demonstrable in hemopoietic tissue during a normal lifespan, they are in process and can be made obvious under anoxic conditions causing cell death followed by an unusual demand for cell replication. Key cellular components of such aged tissues apparently have either lessened resistance to anoxia or a reduction in replicative potential or both. The second alternative interpretation suggests an analogy in vivo to mesenchymal-cell clonal attenuation observed in vitro.

Dissecting the hematopoietic microenvironment. IV: regeneration of splenic microstructure- prerequisites and chronology of reconstruction

A chronologic study was made of whole organ necrosis and subsequent regeneration in the pedicle ligated mouse spleen. The whole organ necrosis involved all but a thin layer of cells including and beneath the splenic capsule. Cellular regeneration issued from these surviving cells and was seen to proceed inward along remaining noncellular reticular fiber tracts throughout the spleen, resulting in complete architectural restoration. Destruction of these fibers resulted in failure of orderly reconstruction of splenic substance. A subcapsular vascular space was made prominent by the ligation and appeared to completely circumscribe the internal splenic substance. Regeneration appeared to begin with cells just central to this space. Reconstruction of the ligated spleen was architecturally complete within 40 days.

Dissecting the hematopoietic microenvironment. V: limitations of repair following damage to the hematopoietic support stroma

Damage and repair of the hematopoietic microenvironment of the spleen was studied using X-irradiation, anoxic necrosis induced by splenic ligation, or a combination of the two, as the destructive agents. Spleen colony number, size and type, 59Fe uptake, and microscopic study of splenic structure were used as means of assessment. The most severe or least repaired damage was induced by high dose irradiation (4000 r), by 1000 r followed immediately by splenic ligation, and by two successive splenic ligations separated by a 30 day recovery period. It was seen that reduction of CFUs lodgment, as measured by f factor, played a very major role in the lesser number of spleen colonies formed after either kind of damage. Following the several treatments, the numbers of spleen colonies formed, their size and their typing as erythrocytic or granulocytic varied independently of each other, suggesting that these functions of the microenvironment, and the cell types responsible for them, are independent of each other. The exhaustion of regenerative capacity displayed by repeatedly ligated spleens suggested a maximal limit for stromal cell replications commensurate with Hayflick's hypothesis.

Ultrastructural lesion in fetal hemopoietic cells following ethanol administration to pregnant mice

Ethanol administration by gavage to pregnant CF1 mice induced myelin-like laminar figures in mitochondria and Golgi complexes of proerythroblasts and erythroblasts in hemopoietically active fetal livers. The laminar figures were observed to be extruded by exotrophy in rare instances. The fetal hemopoietic tissues of sucrose-fed, sham, and untreated pregnant mice rarely displayed laminar figures in immature erythroid cells.

Dissecting the hematopoietic microenvironment. II. The kinetics of the erythron of the S1/S1d mouse and the dual nature of its anemia

An analysis of the S1/S1d mouse for ferrokinetics and fate of peripheral red blood cells has shown the cause of its anemia to be dual in nature. While the S1/S1d produces red cells at a slightly greater rate than its normal littermate, its bone marrow and spleen appear to be operating near their maximal capacity and will reduce their output if anemic stress is partly relieved. The cause of the moderately high level of erythropoiesis in the S1/S1d is a mean daily loss of 2.5--3.0% of its total blood volume via the intestinal tract.

Dissecting the hematopoietic microenvironment. III. Evidence for a positive short range stimulus for cellular proliferation

Experiments were carried out with the intent of defining the nature of the microenvironmental defect which severely limits erythropoiesis in the spleen of the S1/S1d mouse. Chimeric spleens, half S1/S1d and half congenic +/+, supported erythropoiesis in the +/+ region but not in the S1/S1d region, regardless of which genotype was the irradiated, marrow-injected host animal. Implants of normal marrow stroma within the spleens of irradiated S1/S1d mice also supported normal proportions of erythrocytic and granulocytic hematopoiesis. Implants of normal spleen stroma, particularly the capsular portion, into unirradiated s1/s1d mice stimulated erythropoiesis originating from S1/S1d stem cells within and in the immediate vicinity of the implant. The evidence suggests a short range, stromal erythropoietic stimulatory factor which is lacking in the S1/S1d.

Erythroid cell growth from normal and W/WV murine bone marrow on macrophage-coated membranes

Cellulose acetate membranes (CAM) placed in the peritoneal cavity of mice develop a macrophage layer capable of supporting in vivo hematopoietic colonies from intraperitoneally injected bone marrow cells. Modifications allowing for routine morphologic identification of colonies showed that both erythrocytic (E) and granulocytic (G) colonies occur with a consistent E:G ratio of 0.19 +/- 0.037. Stimulating recipients by bleeding or phenylhydrazine injection did not produce a significant change in the total number of colonies and a reduction in granulocytic colonies so that the E:G ratio significnatly increased. Hypertransfusion of donor animals had no effect on the number of erythroid colonies that grew on CAM of average recipients. The total colony-forming ability of bone marrow cells from genetically anemic W/WV mice was found not to differ from that of normal +/+ littermates; however, the E:G ratio of W/WV marrow in bled recipients was significantly lower (p less than 0.01) then that of +/+ marrow. These studies suggest that a CAM system supports an erythroid progenitor which is not affected by hypotransfusion of the donor animal, yet is dependent upon erythropoietin for colony formation, and that it is defective in the W/WV mouse.

The restorative effect of erythropoietic stimulation upon the sublethally irradiated (SLI) hematopoietic stem cell and/or its progeny

Bone marrow cells from sublethally irradiated donor mice injected into supralethally (1000 R) irradiated recipients produced not only many fewer spleen colonies but fewer erythrocytic (E) colonies in relation to the number of granulocytic (G) colonies than did unirradiated donor marrow in similar recipients. This reversal of E:G ratio was partially or completely restored by a strong erythropoietic stimulus in the recipients, whether endogenous, (induced by anemia) or exogenous (injected purified EP). Such a stimulus produced a large increase in total spleen colony numbers in all experiments. An unexpected result was a major increase in granulocytic and megakaryocytic colonies in the spleen and marrow of the erythropoietically stimulated recipients. It was concluded that the sublethal irradiation to the donor either produced or revealed a subpopulation of potential colony forming cells whose cell cycle was slow or temporarily arrested. The added EP (and/or related substances) was proposed to have either overridden or induced repair or radiation defect, or stimulated a small and normally undetectable population requiring high levels of stimulant to induce cycling. The result was the expression of their progeny as colonies, whose differentiative type depended upon the kind of hematpoietic inducing microenvironment in which they had lodged.

Hemopoietic colony studies. V. Effect of hemopoietic organ stroma on differentiation of pluripotent stem cells

In heavily irradiated mice, bone marrow regeneration of either endogenous or exogenous origin was shown to occur in discrete foci comparable to the more intensively studied spleen colonies. The number of endogenous bone marrow colonies was inversely related to dose of whole body X-irradiation. Endogenous marrow colonies were found after higher doses of irradiation than were endogenous spleen colonies. Most of them were granulocytic in nature. Exogenous bone marrow colonies in lethally irradiated mice injected with bone marrow cells were proportional in number to the dose of cells injected, appeared at a time comparable to spleen colonies like which, at 7 or 8 days, they were of single differentiated cell line, either granuloid or erythroid or megakaryocytic, with a small percentage of "mixed" colonies. Whereas erythroid colonies outnumber granuloid colonies in spleen, either in situ or subcutaneously transplanted (E:G colony ratio of about 3.5), granuloid colonies outnumber erythroid in bone marrow (E:G colony ratio of about 0.7). The characteristic E:G colony ratios of spleen and marrow appear more likely to be the result of a hemopoietic organ stromal influence on pluripotent colony forming units (CFU's) than of selective lodgment of committed (unipotent) granuloid and erythroid CFU's in bone marrow and spleen, respectively, as indicated by the following. Bone marrow stem cells (CFU) which had reseeded the marrow cavity of irradiated primary recipients 18-24 hr earlier, were reharvested and retransplanted intravenously into irradiated secondary hosts. The E:G colony ratio of the colonies formed in the spleen of the secondary hosts was typical of primary spleen colonies (2.8), that of the colonies formed in the marrow cavity was typical of bone marrow colonies (0.6). Pieces of marrow stroma containing reseeded CPU's from the contralateral femur of these same primary recipients were implanted by trocar directly into the spleens of other irradiated secondary recipients. Those CPU's that developed in the intrasplenic-implanted marrow stroma yielded an. E:G colony ratio of 0.1. Those that migrated into the contiguous and remote portions of the spleen gave E:G colony ratios of 2.9 and 2.4, respectively. Irradiated marrow stroma and normal spleen CPU's (a 1 mm cube of spleen) were loaded into the same trocar and implanted directly into the spleens of irradiated mice. The spleen CFU's that migrated into the implanted marrow stroma yielded five granuloid and two mixed colonies. The larger number that developed in the host spleen yielded an E:G colony ratio of 2.9 or higher. Of those 19 mixed colonies that bridged the junction of spleen and implanted marrow stroma in each of the above two experiments, in every case, the erythroid portion of the colony was in the splenic stroma, the granuloid portion was in the marrow stroma.