Normal F1 Hybrids Research Articles

Asymmetry in the reproductive interference between two closely related species of spider mites, Panonychus citri and Panonychus osmanthi (Prostigmata: Tetranychidae).

An incomplete species recognition system may cause reproductive interference. Interspecific mating between Panonychus citri and Panonychus osmanthi produced apparently normal F1 hybrid females. However, the F1 females laid few eggs, and the produced eggs did not hatch (suggesting hybrid breakdown). Several common host plants of P. citri and P. osmanthi have been determined, including Japanese pear, peach, and citrus. However, P. osmanthi has been found only on its particular host plants in the genus Osmanthus. To assess the potential for reproductive interference between P. citri and P. osmanthi, we evaluated the competitiveness (1 ♀ × 2 ♂♂) and preference (2 ♀♀ × 1 ♂) of males in mating and guarding behavior and assessed the effect of second mating on offspring paternity using Japanese pear leaf disks. We found that P. citri males were superior competitors. Moreover, the species recognition ability of P. citri males was lower than that of P. osmanthi males, and frequent occurrence of reproductive interference should therefore be expected. In a mixed population (2 ♀♀ × 2 ♂♂), 41% of females copulated with heterospecific males, although the mating superiority of P. citri was not proven. The ratio of effective second mating with conspecific males after heterospecific mating was higher in the crosses to P. citri females (77.8%) than P. osmanthi females (14.3%). Therefore, P. citri females had more chance than P. osmanthi females to recover from the fitness cost imposed by heterospecific mating through subsequent conspecific mating. To date, P. osmanthi has not been detected on host plants other than Osmanthus species. Reproductive interference by P. citri males may therefore narrow the range of host plants available for P. osmanthi.

Molecular genetic analysis of off-type plants identified from normal F1 hybrid cultivars of sweet pepper (Capsicum annuum L.)

SummaryOff-type plants occasionally appear when growing F1 hybrid cultivars of sweet pepper (Capsicum annuum L.). In this study, possible genetic factors responsible for the appearance of off-types were evaluated using two off-type sweet peppers selected out of 120 F1 hybrids. The general morphology of off-type plants showed a stunted stature, narrow leaf shape, and small round-shaped fruits. We hypothesised that these off-type plants might have arisen by inadvertent self-pollination of maternal parental lines, since most sweet pepper F1 hybrids are known to be produced by hand-emasculation. Indeed, none of the sweet pepper cultivars analysed in this study contained male-sterile cytoplasm, confirming that cytoplasmic male-sterility was not used during F1 hybrid seed production. If the off-type plants were derived from self-pollination of maternal lines, the genetic make-up of the off-type plants should be different from that of normal F1 hybrids. However, the RAPD and SSR marker amplification profiles of off-type and normal F1 hybrids showed no polymorphism, whereas one RAPD and five polymorphic SSR markers were identified among five other F1 sweet pepper cultivars, indicating that the genetic make-up of the off-type and normal F1 hybrids were almost identical. Furthermore, two SSR markers that showed heterozygosity in both off-type and normal F1 hybrids, segregated in the self-pollinated progenies of both off-type and normal F1 hybrids, indicating that the off-type plants were not maternal inbred lines. Taken together, these results suggest that the off-type F1 sweet pepper plants could have arisen due to other environmental factors or by infection with an unknown pathogen.

Immunological tolerance and tumor rejection in embryo-aggregated chimeric mice – Lessons for tumor immunity

BackgroundRejection of transplanted tumors by the immune system is a rare event in syngeneic hosts, and is considered to be dependent on the local interaction of defensive immune reactions and tumor tolerance mechanisms. Here, we have enlisted the aid of a unique set of embryo-aggregated lineage chimeric mice derived from C57/BL6 and FVB donors to study the interplay between local and systemic tumor immunity and tolerance in rejection of mouse B16 melanoma cells, syngeneic to the C57/BL6 donor strain.MethodsTwo variants of embryo-aggregated chimeric mice with either variable or no contribution of C57-derived cells to their skin were generated by the fusion of different ratios of morula stage blastomers. Chimeric mice were analyzed for s.c. growth of B16 tumors in comparison to their respective donor strains as well as normal F1 hybrids, and the relative frequencies of cellular components of the immune system by FACS analysis of peripheral blood or lymph node cells.ResultsB16 tumors grew significantly faster in mice with full chimerism in their skin as compared to syngeneic C57 or semi-syngeneic C57 × FVB F1 hosts. In contrast, s.c. tumor growth was either absent or significantly reduced in chimeric mice lacking C57-derived cells in their skin, but tolerant to C57 tissue in other organs. Comparison of the relative frequencies of various immune cells in the periphery via FACS-analysis did not reveal any significant differences between the two types of chimeric mice with respect to their donor strains.ConclusionOur data suggest a complex interplay between mechanisms of local peripheral tolerance and innate antitumor mechanisms possibly involving NK cell allorecognition as a basis for the differential growth or rejection of B16 tumors in these unique chimeric mice, which we suggest to constitute a valuable new model system for the study of immune-mediated tumor rejection.

Studies on unreduced gamete formation in hybrids between tetraploid wheats and Aegilops squarrosa L.

Five accessions of Aegilops squarrosa L. were crossed to nine of tetraploid wheat, and 18 combinations of normal F1 hybrids were obtained. Their meiosis and the frequency of unreduced gamete formation were observed. From cytological observations, unreduced gametes were formed as follows; restitution of the first meiotic division, and normal second division followed by formation of dyads which developed into two fertile 2n pollen grains. Unreduced gametes were formed with high frequency in the following cases; (1) when Triticum carthlicum Nevski was used as female and Ae. squarrosa ssp. strangulata Eig or var. meyeri Griseb. was used as male; (2) when spikes headed relatively later; (3) in spikes of secondary or subsequent tillers. The high frequency of unreduced gamete formation in F1 hybrids between T. carthlicum and ssp. strangulata or var. meyeri is genetically controlled.

Hybrid chlorosis in wheat × rye crosses

Fourteen accessions of rye when crossed to Triticum aestivum cv. C 306 (Ne1ne2ch1Ch2) yielded chlorotic F1 hybrids and six accessions involved in hybrid combination with the same tester produced normal F1 hybrid plants. Two rye accessions, namely, EC 179188 and EC 143825 when crossed to the wheat lines HD 2329 (ne1Ne2ch1Ch2) and NI 5439 (ne1ne2ch1Ch2) also produced chlorosis. The hybrids between T. macha and two rye accessions produced normal plants. Variable degrees of chlorosis were observed among different wheat × rye F1 hybrids. It is suggested that the rye accessions producing chlorosis in combination with wheat cvs. C 306, HD 2329 and NI 5439 (all Ch2-carriers) carry one of the complementary genes for chlorosis. Gene symbol Chr1 is proposed for the chlorosis gene of rye.

Allele-specific expression and total expression levels of imprinted genes during early mouse development: implications for imprinting mechanisms.

Genomic imprinting determines the monoallelic expression of a small number of genes during at least later stages of development. To obtain information necessary for the elucidation of imprinting mechanisms, we assessed the allele-specific expression and total expression level of four imprinted genes during early stages of development of normal F1 hybrid mice utilizing quantitative allele-specific reverse transcription-PCR (RT-PCR) single-nucleotide primer extension assays. The Igf2r and Snrpn genes were activated by the early 4-cell stage and exhibited biallelic and monoallelic expression, respectively, throughout preimplantation development. Thus, with respect to different imprinted genes, epigenetic systems determining monoallelic expression are not uniform in their time of establishment. Biallelic expression of Igf2r was observed in single blastomeres, discounting the possibility of random allelic inactivation at this stage. The closely linked H19 and Igf2 genes were activated after the blastocyst stage and often exhibited biallelic and monoallelic expression respectively in tissues of pregastrulation postimplantation-stage embryos, rather than reciprocal monoallelic modes as observed at later stages. This raises the possibility that imprinting of H19 is involved only in the maintenance and not in the initiation of monoallelic expression of Igf2. Monoallelic expression of Snrpn was observed in each blastomere at the 4-cell stage, demonstrating that the germ line, which exhibits biallelic expression of imprinted genes, must be derived from cells in which imprinting was once manifest.

The use of parabiosis for investigating the mechanism of transplantation tolerance in bone marrow chimeras induced by total lymphoid irradiation

The mechanism of transplantation tolerance in total lymphoid irradiation (TLI)-induced semiallogeneic bone marrow chimeras without clinical evidence of graft-versus-host disease (GVHD) was investigated using the technique of surgical parabiosis. When held in parabiosis with normal BALB/c mice, BALB/c---- (BALB/c x C57BL/6)F1 (BALB----F1) chimeras survived 7-9 days, significantly (P less than 0.001) shorter than the 12-19 day survival of normal F1 hybrids kept in parabiosis with normal BALB, and in contrast to indefinite (greater than 200 days) survival of syngeneic BALB parabiotic partners. When C57 skin grafts were placed on BALB mice held in parabiosis with BALB----F1 chimeras, C57 skin grafts survived 50-60 days, in contrast to 10-14 days in normal BALB recipients (P less than 0.001). Lethal GVHD, induced in sublethally irradiated F1 recipients by 10(7) BALB spleen cells, could not be delayed or prevented by cotransfer of 10(7) to 30 x 10(7) tolerant BALB spleen cells obtained from stable BALB----F1 chimeras. GVHD reactivity of BALB spleen cells isolated from BALB----F1 chimeras tolerant of C57 could not be recovered by depletion of Lyt2 cytotoxic suppressor cells. Taken together, in the absence of suppressive capacity by suppressor cells, these data support functional clonal deletion as the primary mechanism responsible for the maintenance of unresponsiveness to host alloantigens in TLI-induced semiallogeneic chimeras, since no protection against induction of GVHD could be documented in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of parabiosis for investigating the mechanism of transplantation tolerance in bone marrow chimeras induced by total lymphoid irradiation

Abstract. The mechanism of transplantation tolerance in total lymphoid irradiation (TLI)-induced semiallogeneic bone marrow chimeras without clinical evidence of graft-versus-host disease (GVHD) was investigated using the technique of surgical parabiosis. When held in parabiosis with normal BALB/c mice, BALB/c (BALB/c C57BL/6)F1 (BALBF1) chimeras survived 7–9 days, significantly (P < 0. 001) shorter than the 12–19 day survival of normal F1 hybrids kept in parabiosis with normal BALB, and in contrast to indefinite (> 200 days) survival of syngeneic BALB parabiotic partners. When C57 skin grafts were placed on BALB mice held in parabiosis with BALBFl chimeras, C57 skin grafts survived 50–60 days, in contrast to 10–14 days in normal BALB recipients (P < 0. 001). Lethal GVHD, induced in sublethally irradiated Fl recipients by 107 BALB spleen cells, could not be delayed or prevented by cotransfer of 107 to 30 107 tolerant BALB spleen cells obtained from stable BALBFl chimeras. GVHD reactivity of BALB spleen cells isolated from BALBF1 chimeras tolerant of C57 could not be recovered by depletion of Lyt 2 cytotoxic suppressor cells. Taken together, in the absence of suppressive capacity by suppressor cells, these data support functional clonal deletion as the primary mechanism responsible for the maintenance of unresponsiveness to host alloantigens in TLI-induced semiallogeneic chimeras, since no protection against induction of GVHD could be documented in vivo. The transfer of relative unresponsiveness to the host's alloantigens to the normal BALB partner of BALB/BALBFl parabiotic pairs following separation is also compatible with the latter conclusion, although transfer of suppressor cells capable of blocking rejection but not GVHD against the same alloantigens cannot yet be formally excluded.

Genetic Compatibility of Aedes (Protomacleaya) triseriatus with A. (P.) brelandi and A. (P.) hendersoni (Diptera: Culicidae)

Interspecific hybridization was used to examine reproductive compatibility of Aedes (Protomacleaya) triseriatus (Say) with Aedes (P.) brelandi Zavortink and Aedes (P.) hendersoni Cockerell. Most male progeny were sterile intersexes when A. brelandi or A. hendersoni males were crossed with A. triseriatus females. Female hybrids, and males from the reciprocal crosses, were morphologically normal and fertile. Varying percentages of intersex males were observed among progeny when normal F1 hybrids were crossed to either parental species or with other hybrids. Egg and female sterility resulting from a partial incompatibility between A. triseriatus cytoplasm and A. brelandi male-determining chromosome was observed. No evidence of large chromosomal rearrangements such as inversions or translocations was observed in the interspecific hybrids. However, frequency of chiasma in meiotic chromosomes was significantly reduced in hybrids.

Genetically controlled desynapsis in diploid Critesion violaceum and its hybrids with autotetraploid Psathyrostachys juncea

Segregation for chiasma frequency was observed in the progeny of a diploid (2n = 14) Critesion violaceum strain following self-pollination. One S1 plant had normal metaphase pairing with an average of 0.43I + 6.78II, giving a high chiasma frequency, 12.03 per cell. The other S1 plant averaged 7.89I + 3.08II and a low chiasma frequency, 3.47 per cell. Examination of pollen mother cells at early prophases revealed that chromosome pairing was not totally prevented. It was concluded that desynapsis was responsible for the meiotic irregularities observed in the variant progeny. The same phenomena were observed in F1 hybrids of the cross between diploid C. violaceum and an induced autotetraploid (2n = 28), Psathyrostachys juncea. The normal F1 hybrid had a chiasma frequency of 12.81, but the desynaptic hybrid had a chiasma frequency of 6.94. A dosage effect of the desynaptic gene, which was probably recessive, was suggested. The implications and significance of this discovery are discussed.Key words: asynapsis, chiasma, meiosis, intergeneric hybrid.

Acquisition of graft-versus-host reactivity by immature thymocytes in the coexistence of activated macrophages.

The collaborative role of macrophages in the acquisition of the rat graft-versus-host (GVH) reactivity by parental thymocytes was investigated by the popliteal lymph node enlargement assay. The addition of peritoneal macrophages activated by streptococcal bacteria injection resulted in significantly increased GVH reactivity of parental thymocytes, when assayed both in normal F1 hybrid hosts and in those depleted of effective macrophages and lymphocytes. The thymocytes that acquire that alloantigen reactivity in the presence of activated macrophages were shown to be cortisone sensitive and of high density. Hence, the cortisone-resistant and less dense population of thymocytes did not exhibit further reactivity even in the presence of macrophages; however, this subpopulation showed an enriched activity on its own. Moreover, the simultaneous injection of activated macrophages induced a further augmenting effect on the graft-versus-host reaction (GVHR) of freshly peripheralized thymocytes, but did not affect the reactivity of lymph lymphocytes from parental rats thymectomized 15 months previously. These data suggest that activated macrophages play an essential role in the acquisition of alloantigen reactivity by immature thymocytes, and also that the macrophage-dependent thymocytes in the reaction may reside among the subpopulation that is cortisone sensitive, highly dense, short-lived, and freshly peripheralized. The possible nature of immunological maturation of immature thymocytes in the periphery is discussed in relation to cellular interactions with activated macrophages.

Augmenting effect of exogenous macrophages on the rat graft-versus-host reaction in F1 hybrids depleted of macrophages.

The crucial role of macrophages in the generation of the rat graft-versus-host reaction (GVHR) was investigated in normal and macrophage-depleted F1 hybrid rats. The addition of exogenous macrophages, colloidal carbon, or lipopolysaccharide (LPS) resulted in a great augmentation of GVH reactivity of parental lymph node cells in normal F1 hybrid rats. Uptake of foreign materials by F1 macrophages exerts a biphasic action on the GVHR, activating or blocking the biological activity. This depends on the time of injection of foreign materials. To define the extent of macrophage dependence in the GVHR, the additive effect of exogenous macrophages on the reaction was investigated in F1 hybrid rats depleted of effective macrophages and lymphocytes, which had received preliminary host irradiation and colloidal carbon injection. In F1 hybrids depleted of macrophages and given injections of parental lymph node cells depleted of macrophages, the addition of exogenous F1 macrophages resulted in a much higher reaction than did lymphocytes alone. The data suggest that macrophage-induced augmentation of the reaction may be a reflection of the regulatory function of macrophages in the cellular interactions between parental GVH-reactive lymphocytes and alloantigen-bearing host cells in vivo.

Cellular and genetic control of antibody responses. V. Helper T-cell recognition of H-2 determinants on accessory cells but not B cells.

Requirements for helper T-cell recognition of H-2 determinants expressed on adherent accessory cells and on B cells was individually assessed in the anti-hapten PFC responses to TNP-KLH. Complicating allogeneic effects were minimized or avoided by the use of helper T cells from normal F1 hybrids, parent leads to F1 chimeras, and F1 leads to parent chimeras. The results of both in vitro and in vivo experiments demonstrated that: (a) helper T cells are not required to recognize the identical H-2 determinants on both accessory cells and B cells; (b) helper T cells are required to recognize K or I-A region-encoded determinants expressed on accessory cells; (c) no requirement was observed in vitro or in vivo for helper T-cell recognition of B-cell-expressed H-2 determinants; and (d) no requirement was observed for H-2 homology between accessory cells and B cells. The absence of required helper T-cell recognition of the identical H-2 determinants on both accessory cells and B cells was demonstrated in two ways: (a) naive of KLH-primed (A x B)F1 hybrid helper T cells collaborated equally well with B cells from either parentA or parentB in the presence of accessory cells from either parent; (b) A leads to (A x B)F1 chimeric spleen cells depleted of accessory cells collaborated equally well with accessory cells from either parentA or parentB, even though the B cells only expressed the H-2 determinants of parentA. A requirement for helper T-cell recognition of K or I-A region-encoded H-2 determinants on accessory cells was also demonstrated in two ways: (a) (A x B)F1 leads to parentA chimeric spleen cells depleted of accessory cells collaborated with accessory cells from parentA but not parentB; and (b) (A x B)F1 leads to parentA chimeric helper T cells collaborated with normal F1 B cells only in the presence of parental or recombinant accessory cells that expressed the K or I-A region-encoded determinants of parentA. Although restricted in their ability to recognize H-2 determinants on accessory cells, it was demonstrated both in vitro and in vivo that (A x B)F1 leads to parentA chimeric helper T cells were able to collaborate with B cells from either parentA or parentB. In vitro in the presence of accessory cells from parentA, (A x B)F1 leads to parentA chimeric helper T cells collaborated equally well with B cells from either parent. In addition, the inability of (A x B)F1 leads to parentA chimeric helper T cells to collaborate with (B + accessory) cells from parentB was successfully reversed by the addition of parentA SAC as added accessory cells. In vivo, upon the addition of parentA accessory cells, (A x B)F1 leads to parentA chimeric helper T cells collaborated with parentB B cells in short-term adoptive transfer experiments.

Genes in diploid triticinae compensating for the low temperature regulating gene Ltp in chromosome 5D of Triticum aestivum

Hybrids of Triticum aestivum (monosomic 5D or ditelosomic 5DL) x T. speltoides (= Ae. speltoides) showed that the genotype of T. speltoides carries gene(s) which can partially compensate for the expected decrease in chromosome association at low temperatures (10°C) in the absence of chromosome 5D. In hybrids of T. aestivum (normal, ditelosomic 3DL or ditelosomic 3DL-monosomic 5D) x T. longissimum (= Ae. sharonensis), this compensation was not observed.In normal F1 hybrids of T. durum x T. longissimum partial chromosome association occurred at 10°C and this stabilizer effect may be explained by the presence of a Ltp-like gene on chromosome 5A. When a line of T. durum carrying a homozygous translocated 5B-5D chromosome was used in the crosses an even higher chromosome association was observed.These results suggest either the existence of a promoter gene for chromosome association in the 5D translocated segment or the loss of a weak suppressor gene in the removed segment of 5B. It was concluded that the translocated 5D segment did not carry the Ltp stabilizer gene.

Immune response in malnutrition. Effect of protein deficiency on the DNA synthetic response to alloantigens.

To evaluate the DNA synthetic response to alloantigens by lymphocytes from mice fed diets with normal (27%) and low (8%) protein content, we quantitated the uptake of 125IUDR in spleens of lethally irradiated adult F1 hybrids injected with cells with parental C57BL/6 donors kept on either diet. Thymocytes, spleen and lymph node cells from protein-restricted parental mice synthesized higher amounts of DNA than those from normally fed controls. Added thymocytes from either malnourished or normal F1 hybrids had similar inhibitory effects on the response of an active parental inoculum. The results indicate that cells from mice kept on a moderately protein-deficient diet for 3--5 weeks after weaning, have increased capacity to proliferate in response to alloantigens, suggesting a high proportion of reactive cells and/or changes in the ratio of the interacting cell populations in their lymphoid organs.

An analysis of graft-versus-host disease in Syrian hamsters. II. The epidermolytic syndrome: studies on its pathogenesis.

The epidermolytic syndrome that can be obtained at will in F(1) hybrid hamsters by the cutaneous inoculation of adequate doses of parental strain lymphoid cells has been investigated to determine whether the cutaneous lesions are due to an autoimmune process arising from the severe, initial GVH reactions in the skin. It was amply demonstrated that inoculation of donor cells into the skin was of crucial importance to the development of epidermolysis. Parental strain lymphoid cells in similar doses delivered by any other route into normal F(1) hybrids failed absolutely to incite the acute syndrome. If "immune lymphocyte transfer" reactions incited by donor cells in the host's skin were surgically removed at timed intervals after inoculation, only complete excision within 24 hr prevented the appearance of epidermolysis in F(1) hybrid hosts, indicating that inoculated donor cells must remain within the confines of the skin for approximately 24 hr in order to evoke the disease, persistence for longer periods of time being unnecessary for the subsequent course of the disease. However, reconstitution experiments involving the intramuscular inoculation of suspensions containing mixtures of donor cells and host lymphoid cells, in the presence or absence of epidermal cells, unequivocally indicated that no intimate exposure of lymphoid cells to putative skin-specific antigens was essential. Similarly, the elicitation of generalized epidermolysis in F(1) hybrids irradiated with 300 r and then inoculated intravenously with donor cells casts further doubt on the pathogenic importance of the skin as a source of tissue-specific antigen. The results of subsequent experiments indicated that host leukocytes, rather than parenchymal cells of the dermis or the epidermis, were important contributors of the transplantation antigenic stimulus. Moreover, a series of experiments, using (CB x MHA)F(1) hybrid hosts that had been lethally irradiated and reconstituted with bone marrow cells from ALS-treated MHA donors, indicated that from 6 to 10 wk after reconstitution-when direct and immune lymphocyte transfer reactions showed a virtual absence of native F(1) leukocytes from the circulation-donor cells obtained from specifically sensitized MHA donors were completely ineffective in inducing epidermolysis, while equivalent lymphoid cell inocula derived from CB donors evoked the cutaneous disease irrespective of the time elapsed since reconstitution. To explain these findings it is postulated that in hamsters, the primary targets in graft-versus-host disease incited by the intracutaneous inoculation of donor cells are leukocytes originating in bone marrow or lymph node, or both.

Inheritance and Utilization of Five Dwarfs in Pearl Millet (Pennisetum typhoides) Breeding1

Height measurements were made on over 39,000 parent, F1, F2, and backcross plants of hybrids involving five dwarf and four normal inbreds of pearl millet, grown in replicated randomized blocks. F1 hybrids between four of the dwarfs were as tall as normal × dwarf hybrids, proving that these dwarfs carried different recessive genes for dwarfness. One dwarf × dwarf hybrid was little taller than its taller dwarf parent, suggesting that both carried similar dwarf genes. Most dwarf × normal F1 hybrids were significantly taller (up to 37%) than their normal parents. Inheritance of dwarfness in D1 and D2 appeared to be conditioned largely by one or two recessive genes. Near‐normal F2 distribution curves and minimum‐gene‐number estimates indicated that dwarfness in D3, D4, and D5 was controlled by more than two recessive genes. When transferred to a near‐isogenic background, dwarfness in D1 and D2 was controlled by single but different recessive genes, named d1 and d2, respectivel.Gahi‐2 seed, produced by harvesting all seed from a field planted to a mixture of equal numbers of seeds of D1, D2, D3, and D4, contains about 75% of tall hybrids and yields nearly as much as Gahi‐1. Cytoplasmic malesterile dwarfs can be used as females to facilitate singlecross seed production. They will give tall hybrids if tall or different dwarf males are used. By using males carrying the same dwarf genes, short, extra‐leafy, high‐quality forage hybrids can be produced.

Evidence for Stem Cells in the Peripheral Blood of Mice

Abstract Leukocytes from the peripheral blood of normal F1 hybrid mice have been successfully used to promote survival of lethally irradiated parent and closely related homologous animals. Identification of donor-type red cells and leukocytes has been established on samples of blood taken from several long-term survivors. Histologic data and serologic typing of cells from lymph nodes, bone marrow, and spleens of chimeras killed early after irradiation and treatment established that injected peripheral leukocytes had transplanted and were proliferating into lymphocytes, granulocytes, and erythrocytes. Fe59 was taken up by red cells and spleens of leukocyte-injected mice but not by tissues of radiation control animals. The newly formed, Fe59-labeled erythrocytes were hemolyzed by immune serum specific for donor-type antigens.