Five-year survival in Hodgkin's disease. The prospective value of immune status at diagnosis

Immune status was measured in 47 previously untreated patients with Hodgkin's disease. For all patients, a 5-year follow-up was established. Immunologic capacity was measured by delayed-type hypersensitivity tests to common recall-antigens; enumeration of T- and B-lymphocytes in the peripheral blood; in vitro lymphocyte responsiveness to mitogens, antigens, and allogeneic lymphocytes; and serum levels of immunoglobulins. Compared with healthy controls, skin reactivity was decreased in the patients (P less than 0.05), but was not a prognostic marker with regard to survival. Total lymphocyte counts and the numbers of T- and B-cells did not differ between surviving and deceased patients. Decreased in vitro lymphocyte responsiveness to phytohemagglutinin and impaired responding capacity of patients lymphocytes in the mixed lymphocyte culture (MLC), used as markers, were a poor prognostic sign (P less than 0.001). The relevant clinical parameters with regard to 5-year survival were age, stage, and B symptomatology (P less than 0.005). The prognostic information supplied by age plus responding capacity in the MLC exceeded the predictive value of any combination of clinical parameters. Lymphocyte stimulation to pokeweed mitogen and antigens, stimulatory capacity of patients' lymphocytes in mixed lymphocyte cultures, the spontaneous DNA-synthesis, and immunoglobulin levels, did not provide prognostic information. The use of mixed lymphocyte cultures in staging patients with Hodgkin's disease may refine the prognostic information supplied by age, stage, and symptomatology.

The French-American-British (FAB) classification of leukemia. The Pediatric Oncology Group experience with lymphocytic leukemia

The Pediatric Oncology Group institutions initiated extensive subclassification of cases of acute lymphocytic leukemia (ALL) at diagnosis into laboratory-designated categories. Included was a French-American-British (FAB) classification of all new patients, which was reviewed by a central six-member committee. In addition, on the basis of immunologic criteria, patients were defined as having T-, B-, pre-B-, or "null" cell leukemia. Slides from 617 patients were reviewed. Five hundred forty-six (88.5%) were classified as L1, 51 (8.3%) were classified as L2, 9 (1.5%) were classified as L3, and the remainder could not be assigned. Concordance within the committee was good: in 71% of the cases the committee was unanimous, and in an additional 17% only one member disagreed. In only 11 cases (1.8%) was diagreement such that a majority classification could not be assigned. Institutions assigned L2 more frequently. There was a strong correlation with L3 for B-cell disease only. However, four patients had unequivocal B-cell disease and unmistakable L1 morphologic type, whereas one and had L3 morphologic features and had non-B-cell disease. There was no correlation between the other immunologic markers or periodic acid-Schiff stain and FAB classification, nor between L1 or L2 and risk factors. However, for the 248 null cell and pre-B-cell patients, L2 was more frequent among patients in the poor-risk group (P = 0.008). The time to first failure was significantly shorter for patients with L3 morphologic type. The induction failure rate of L2 patients was significantly greater than that of L1 patients (P = 0.016). With analysis of the duration of remission and adjustment for risk factors, the impact of L2 morphologic characteristics on outcome was not significant (P = 0.18) in null cell patients. Even unadjusted for risk factors, there was no impact of L2 morphologic type on outcome in the pre-B-cell phenotype. It can be concluded that other risk factors overshadow the impact of L1 and L2 morphologic features in predicting duration of remission.

Modulation of in vitro myelopoiesis by LGL: different effects on early and late progenitor cells

We describe here the modulatory activity of human peripheral blood natural killer (NK) cells on the growth and differentiation of myeloid progenitor cells at different stages of maturation. NK-enriched cell fractions containing 54 to 75% large granular lymphocytes (LGL) and displaying high levels of NK activity significantly inhibited the growth of late (7 day) granulocyte-macrophage colony-forming cells (CFU-GM) from about 50% of normal human bone marrow samples. However, the same fractions strongly enhanced the growth of early (14 day) stem cells from peripheral blood. Enhancing activity on early CFU-GM from blood was greater in highly purified NK cell preparations containing 96% LGL than in NK-depleted T cell preparations from the same donors. Analogous to the results when using the NK-enriched fractions, the NK-purified preparations inhibited late CFU-GM and stimulated the early ones. We conclude from these observations that human LGL have a modulatory effect on myelopoiesis depending on the maturation stage of the progenitor cell.

Accumulation of immature B and null lymphocytes in the periphery after intraperitoneal administration of traditional Chinese medicine, xiao-chai-hu-tang (Japanese name: shosaiko-to)

Accumulation of lymphocytes after an intraperitoneal (ip) injection of a traditional Chinese herb medicine, XIAO-CHAI-HU-TANG (Japanese name: shosaiko-to), was investigated. Shosaiko-to induced marked accumulation of lymphocytes rather than macrophages in the peritoneal cavity of ICR mice, whereas various kinds of irritants, e.g. proteose-pepton, Escherichia coli lipopolysaccharide (LPS), OK-432 and Corynebacterium parvum, induced preferential accumulation of macrophages rather than lymphocytes. By means of analysis using two-color fluorescence-activated cell sorter (FACS), it was revealed that the increased lymphocyte subpopulations not only in the peritoneal cavity but also in the spleen of C3H/He mice by the injection of shosaiko-to were comprised of both immature B (IgM+ and IgD-) and null (thyl- and Ig-) cells. This effect of shosaiko-to was observed in other C5 normal strains, C3H/HeJ (LPS-nonresponder), C57BL/6, BALB/c and athymic nu/nu (ICR background) mice, but not in C5 deficient strains, AKR/J, A/J and DBA/2 mice, indicating that the accumulation of immature B and null cells in the periphery induced by shosaiko-to is closely related to the complement system.

Capping of leukemic cells with monoclonal anti-HLA-A,B,C related to prognosis in childhood acute lymphoblastic leukemia

Capping of leukemic cells with a monoclonal antibody against HLA A,B,C determinants was studied in 53 cases of childhood acute lymphoblastic leukemia (ALL). Determination of the percentages of capped cells after different times of incubation with anti-HLA A,B,C show that T ALL and common ALL do have quite different kinetics of HLA capping. In T ALL all cases reach levels of percentage of capped cells above 30%, in common ALL only 11 of 31 cases cap well. Dilution of the antiserum in 6 common ALL cases results in an increase of capped cells, but the original kinetics of the common ALL capping remain. ALL cases with capping curves above 30% have a worse prognosis (shorter continuous complete remission) than cases with capping curves below 30% in the total group as well as in the non-high-risk group.

Preliminary clinical trial of autologous bone marrow transplantation after in vitro monoclonal antibody and complement treatments in null cell-type acute lymphocytic leukemia

Autologous bone marrow transplantation (BMT) in null cell-type acute lymphocytic leukemia (Null-ALL) was carried out after depletion of leukemia cells from transplanted bone marrow. Patients' autologous bone marrow cells were harvested during remission and treated in vitro with complement and three monoclonal antibodies (NL-1, NL-22 and HL-47) reactive to Null-ALL cells, and then cryopreserved. Three patients were transplanted with the antibody-treated bone marrow cells during the first remission period after preconditioning with intensive chemotherapy and total body irradiation, while transplantations in two other patients, who were in poor clinical condition, were done during the fourth remission period and the third relapse, respectively. Good preservation of hematopoietic stem cells after antibody treatment and cryopreservation of bone marrow cells was demonstrated in all five cases studied. Clinically, prompt recovery of white blood cells and platelets was observed in the three patients who received BMT during the first remission period; two of them have continued remission (2 and 15 months), while the other relapsed after 7 months of remission. these results suggested that autologous BMT with these three antibodies may be an effective mode of therapy for Null-ALL patients.

Immune senescence: effect of age, sex and health on human blood mononuclear subpopulations

The respective influence of age, sex and health states on peripheral blood mononuclear subpopulations has been investigated in 194 institutionalized subjects. The "ill group' includes patients with various diseases and the "reference group' was referred to admission criteria for immuno-gerontological disease. A decline of total mature T-cell (OKT3) and helper T-cell (OKT4) proportions with ageing has been found only in the ill group and remains stable in the reference group. This age-dependent decline should represent either a susceptibility for illness or a consequence of higher incidence of illness with ageing. Suppressor-cytotoxic (OKT8), B- and T-activated (OKIa1), null (OKM1), and early E-rosette forming cells do not vary with ageing in both groups. It has been established previously that women have higher values of the percentages of early E-rosette forming cells.

[Effect of bacterial antigens on the functional capacity of immunocompetent cells]

The study of some characteristics of the immune status of healthy donors has revealed that the quantitative characteristics of T-, B- and O-cells directly correlate with the total content of lymphocytes in the peripheral blood. Essential differences in the values of the characteristics indicating the natural resistance of the body (C'H50, IgM, phagocytic activity, phagocytic index) in the donors with a lower or higher (in comparison with the average value) level of lymphocytes in the peripheral blood. In healthy donors no essential changes in the capacity of T- and B-lymphocytes for rosette formation after their incubation with Pseudomonas aeruginosa have been detected.

Characterization of hematogenous cellular constituents of the murine decidua: a surface marker study

Decidual tissue, which includes typical (stromal type) decidual cells as well as infiltrating leukocytes, appears to play a local immunoregulatory role in the maintenance of pregnancy in nature. The present study evaluated the contribution of numerous leukocyte subsets characterized on the basis of morphology combined with cell surface markers to the development of murine decidua during syngeneic (CBA female X CBA male) and allogeneic (CBA female X C57BL/6 male) pregnancy. Collagenase dispersed decidua were subjected to total and differential counts and cell surface labeling for a radioautographic identification of various markers: S-IgM on B cells, Thy-1 on T cells, neither marker on null lymphocytes, Lyt- (1 or 2 or 1,2) antigens on T cell subsets, Mac-1 and I-A on macrophages, using 125I-labeled monoclonal antibodies or a sandwich labeling with 125I-protein A. The total cellularity of decidua basalis showed a biphasic rise in both pregnancies, with peaks on day 11 and days 15 and 16, but the allopregnant decidua showed a higher accumulation of all cell types indicating that an allogeneic conceptus causes an augmented deciduogenesis. The number of decidual cells, the most frequent cell class, rose to a peak on day 11 followed by a decline possibly due to cell death. The number of lymphocytes, the next frequent cell class, showed a parallel pattern initially, followed by a sharp secondary rise on day 16. This rise may be due to a withdrawal of progesterone, an antiinflammatory hormone. Null cells predominated amongst decidual lymphocytes (45-80%), as well as in the progestational endometrium (53%), indicating a hormonal control of their accumulation. The frequency of B cells was low (10-13%) and T cells (25-45%) comparable to that in the blood, with Lyt-1 only class being the most common T cell subset. Allopregnant decidua also showed a late rise in the total number of Lyt-2 only cells which may have a suppressor function. Macrophages, the next common leukocyte class, all expressed Mac-1. Their number rose to a plateau by day 12, but at a higher level in allopregnancy. I-A (needed for antigen presentation) was expressed by an increasing proportion (5-60%) of macrophages with advancing gestation. These findings provide a basis for further functional studies.

Immunocytochemical evidence of common-ALL antigen in null-ALL

4 cases of acute lymphoblastic leukaemia (ALL), diagnosed as null-ALL by indirect immunofluorescence using monoclonal antibodies, were similarly investigated using a sensitive immunoperoxidase method. The Avidin-Biotin system was employed. The immunoenzymatic results were in agreement with those obtained with immunofluorescence techniques for all antigens except common-ALL (C-ALL). The C-ALL antigen, recognized by the J5 antibody, was detected only by the immunoperoxidase method on cell membranes of the 4 ALL. This paper discusses the possibility of false negative results in testing for C-ALL antigen by conventional indirect immunofluorescence as suggested by refined immunocytochemical screening. Moreover, the ability of the immunoperoxidase system to identify antigens on cell membranes, even at very low density, is discussed. The clinical significance of the presence of C-ALL antigen at weak intensity in cases of null-ALL is also considered.

Null cell identification and characterization with OKT16: an anti-p40 monoclonal antibody

A murine monoclonal antibody, OKT16, specific for human lymphocytes of T lineage, was isolated by standard immunization and hybridization techniques. The distribution of the antigen defined by OKT16 was similar to the antigen reactive with monoclonal antibodies 3A1 and WT1. This identity of antigen targets was confirmed in an enzyme-linked immunosorbent assay system and by sequential immunoprecipitation. Under reducing conditions, OKT16 reacted with an antigen of 40K daltons; however, under nonreducing conditions this antigen appeared as an 84K-dalton molecule, which suggests that the p40 antigen exists as a disulfide-linked dimer. By indirect immunofluorescence, OKT16 reacted with a greater fraction of nonrosetting, non-B (null) lymphocytes than with antibodies to other T cell-specific proteins. Two-color immunofluorescence demonstrated the coexpression of the T16 antigen and the C3bi receptor on most null cells. The T10 antigen (found on cortical thymocytes and activated peripheral T cells) was restricted to most T16-bearing null cells and expression of the Fc receptor for aggregated IgG (defined by monoclonal antibody 73.1) was restricted to a major subset of T16-bearing null cells. The T cell-specific markers defined by OKT8, OKT11, and OKT17, as well as the monocyte marker defined by OKM5, were expressed by smaller subsets of OKT16-reactive null cells. These studies support by phenotypic analysis the functional heterogeneity ascribed to null cells. The 40K-dalton T16 antigen has the most extensive null cell representation of all the T lineage markers described to date.

An analysis of the presence of Fc receptors on bone marrow lymphoblasts in acute lymphoblastic leukemia. A Pediatric Oncology Group study

The presence or absence of the Fc receptor (FcR) on bone marrow lymphoblasts was evaluated in 279 cases of acute lymphoblastic leukemia (ALL) by member institutions of the Pediatric Oncology Group (POG). The case material was classified as follows: 19 cases of positive (greater than or equal to 20% +), 24 additional cases as intermediate (greater than or equal to 10% but less than 20%), and the remaining 236 cases as negative (less than 10%). Intermediate and positive cases were relatively equally distributed between null cell leukemia and pre-B-cell leukemia, and there were one intermediate and two positive T-cell cases. One of two cases of B-cell leukemia was also positive. There were no distinguishing clinical or laboratory characteristics which distinguished the FcR+ cases, nor was the FcR of prognostic significance within ALL as a group or within immunologically defined phenotypes.

Null cell immunoregulation in SLE

Fresh normal T cells do not lyse MDA-157 target cells. Normal null cells, cultured for 4 days with MDA-157 stimulators, and then mixed overnight with fresh normal T cells, induce cytotoxicity on MDA-157 targets and suppressor activity in the T-cell acceptor population. With the same normal acceptor T cells, MDA-157 activated null cells from 13/18 patients with Systemic Lupus Erythematosus (SLE), unlike activated cells from a disease control population, induce little or no T-cell cytotoxicity or suppression. These results provide further evidence for abnormal null cell function in SLE.

Multimarker phenotypic characterization of adult and childhood acute lymphoblastic leukaemia: an Italian multicentre study

A multicentre phenotypic study was carried out in Italy combining conventional immunological techniques with monoclonal antibody (MoAb) analysis in 190 cases of adult and childhood acute lymphoblastic leukaemia (ALL), in an attempt to define better the lineage relationship of the neoplastic cells. Of the 140 children evaluated, 79.3% expressed the common ALL (cALL) antigen (all analyses performed by MoAb), 11.4% were T-ALL and 9.3% were non-T, non-B, non-common ('null') ALL. The proportion of adult cALL cases was slightly lower (64% of the 50 cases studied) than that of childhood ALL, whilst the incidence of T-ALL was significantly higher in adults than in children (26% v. 11.4%, P less than 0.05). Because of the high proportion of cALL cases, the incidence of 'null' ALL in adult patients was similar (10%) to that of children, and lower than previously reported. The recognition of early pre-T-ALL cases (T1+, RFT2+, T10+, T6-, T11-, E-) contributed to the overall low proportion of 'null' ALL; prior to the use of MoAb, such cases would probably have been classified as undifferentiated acute leukaemia or 'null' ALL. The search for B-cell-related markers showed that the incidence of pre-B-ALL cases (cytoplasmic immunoglobulin positive cases) was similar in adults and in children (25.6% and 32%, respectively). Furthermore, the great majority of cases studied expressed the BA-1 antigen (92.8% of adults and 79% of children), whilst the BA-2 antigen was found in 53% of cases (tested only in children), confirming a hierarchy in the expression of B-cell related markers in cALL: BA-1, BA-2, CyIg. Several of the 'null' cases also expressed the BA-1 antigen on a variable proportion of cells, pointing to a possible B-cell origin of the blasts. This multicentre study shows that both in adult and in childhood ALL the combined use of conventional immunological markers and of a panel of MoAb allows identification of the cell lineage of the great majority of cases, thus reducing the number of 'null' ALL. Furthermore, these findings suggest that practically all cases of ALL belong either to the T or to the B cell compartment and that the neoplastic cells appear blocked at different levels along the lymphoid differentiation pathway.

Effects of cyclosporine in experimental cryptococcal meningitis

We studied the effects of cyclosporine on experimental cryptococcal meningitis. Like cortisone, cyclosporine depressed the highly effective defense mechanisms of normal rabbits against inoculated Cryptococcus neoformans, causing them to develop progressive, fatal cryptococcal meningitis. Unlike cortisone, which causes a striking reduction in leukocytes in cerebrospinal fluid, cyclosporine depressed mononuclear cell function rather than numbers. Interleukin 2, a primary target for the immunodepressive action of cyclosporine, appears to be of central importance in central nervous system defenses against cryptococci. The findings suggest that humans receiving cyclosporine are likely to suffer increased incidence of cryptococcal infection.

SIg-E- ("null-cell") non-Hodgkin's lymphomas. Multiparametric determination of their B- or T-cell lineage

The authors performed immunophenotypic, functional, and molecular analysis of the neoplastic cells from 20 cases of SIg-, E-("null-cell") non-Hodgkin's lymphoma (NHL) in order to determine their lineage, better define this category of NHL, and evaluate the lineage specificity of selected phenotypic markers and the individual and collective utility of these approaches. They assigned 4 cases to the T-cell lineage, and 15 cases to the B-cell lineage, and 1 case remained indeterminant on the basis of immunophenotypic analysis. The cells from 2 cases assigned to the T-cell lineage expressed unusual phenotypes, but their T-cell derivation was confirmed by the demonstration of helper function in vitro. The 15 cases assigned to the B-cell lineage expressed a variety of B-cell-associated antigens, consistent with various stages of B-cell differentiation. Monoclonal antibodies OKT3, OKT4, OKT6, and OKT8 exhibited T-cell lineage restriction; and monoclonal antibodies OKB2, BL1, and B1 exhibited B-cell lineage restriction. Ia, TdT, cALLa, OKT9, and OKT10 exhibited lineage infidelity. Southern blot analysis for immunoglobulin heavy chain gene rearrangements confirmed 18 of the 19 lineage assignments made by immunophenotypic analysis and suggested that the 1 case of indeterminate phenotype was a B-cell neoplasm. One T-cell (OKT3+, T4+) neoplasm exhibited rearranged immunoglobulin heavy chain genes. Thus, neither immunophenotypic analysis nor the demonstration of rearranged immunoglobulin heavy chain genes alone permitted the satisfactory lineage assignment of every case of SIg-, E- NHL. However, combined immunophenotypic, functional, and genotypic analysis allowed us to assign every SIg-, E-NHL to the B- or T-cell lineage and to demonstrate that truly "null-cell" NHLs are probably very uncommon.

Cells and mediators which participate in immunoglobulin synthesis by human mononuclear cells. I. The obligatory requirement of null lymphocytes in the synthesis of immunoglobulins in vitro

The circulating mononuclear cells of normal adult human volunteers were fractionated into T and non-T lymphocytes. The T cells were then fractionated into TM and non-TM cells and the non-T cells were further fractionated, by both positive and negative isolation, into B cells and null cells. Culture of non-T cells, TM cells, and PWM for 7 to 8 days resulted in cytoplasmic Ig (cIg) synthesis by all B cells, as detected by immunofluorescence. However, culture of either purified B or null cells with TM cells and PWM resulted in a marked reduction (75%) of cIg-synthesizing cells. The addition of monocytes did not enhance cIg synthesis. Culture of reconstituted B and null cells with TM cells and PWM restored the capacity to synthesize cIg to the cells. It is concluded that null cells are required, as well as TM cells and PWM, for cIg synthesis by B cells.

[Immunocytochemical indices of the measles vaccinal process]

To study the immune responsiveness of children in the measles vaccinal process, the cytochemical methods for the identification of immunocompetent cells have been used. The investigations have been made in children aged 1.5-4 years, immunized with live measles vaccine prepared from strain l-16. The results of these investigations indicate that the development of specific antiviral postvaccinal immunity is characterized by transitory changes in the populations of T-, B- and O-lymphocytes; such changes are accompanied by not only quantitative, but also qualitative changes of individual populations.

Functional aspects of T-lymphocyte subsets in pregnancy

Several recent reports have suggested that a decrease in circulating T helper cells may contribute to the relative immunodeficiency of pregnancy. To investigate the significance of these findings, 90 pregnant women were evaluated. The results of this study indicate that although pregnant women have a decreased proportion of T helper cells, they do have adequate T helper cell function as determined by an in vitro immunoglobulin synthesis assay and a T-lymphocyte colony-forming assay. Based on these studies it is unlikely that decreased numbers of T helper cells are primarily responsible for the immunodeficiency of pregnancy.

Lymphoid interstitial pneumonia: findings at bronchoalveolar lavage

In a patient with lymphoid interstitial pneumonia (LIP), confirmed by open lung biopsy, immunological derangement was evaluated using bronchoalveolar lavage fluid and peripheral blood. In the bronchoalveolar lavage fluid there were 20% null cells, 0% B cells, 77% alveolar macrophages and 3% T cells; in the peripheral blood these were 12% null cells, 43% B cells, 26% mononuclear phagocyte system cells, 2% double marker cells and 17% T cells. Thus there was T cell depletion and null cell increment in bronchoalveolar lavage, in contrast to T cell depletion and increment of B cells and mononuclear phagocyte system cells in the peripheral blood.

Changes in the host natural killer cell population in mice during tumor development. 1. Kinetics and in vivo significance

Our earlier studies revealed an increase in the level of null (surface IgM-negative, Thy 1-negative) lymphocytes in mice shortly after tumor transplantation and before the clinical appearance of spontaneous mammary tumors. The present study examined the splenic natural killer (NK) cell activity as well as the incidence of NK lineage cells in these hosts, since NK cells are considered to be a subset of null lymphocytes. Splenic NK activity against YAC-1 lymphoma targets was measured with a 4-hr 51Cr-release assay in CBA mice transplanted ip with 10(6) Ehrlich ascites tumor (EAT) cells, in elderly C3H mice prior to and during the growth of spontaneous mammary tumors (SMT) and in young C3H mice transplanted sc with 5 X 10(6) SMT cells or 10(6) cells from two syngeneic mammary tumor lines (T-58 and MT-2) of recent origin. In EAT-transplanted mice total NK activity in the spleen increased rapidly to a peak (11-fold) at 3 days, coincident with the null cell rise, but then declined to subnormal levels by Day 7 when the null cell level was still high. A similar pattern of activity was exhibited by intratumor lymphocytes isolated from the EAT. In SMT-transplanted mice splenic NK activity showed a small rise at Day 3, followed by a drop to below normal at Day 7, subnormal levels lasting for the tumor life span. Similar results were noted in T-58- or MT-2-transplanted mice. Null lymphocytes recovered during the peak NK activity from the spleen of 3-day EAT-bearing mice, when mixed with 10(6) EAT cells at 25:1 E:T ratio and adoptively transferred into fresh mice in a Winn type assay either ip or sc, completely prevented tumor development indicating a high enrichment of NK cells functionally effective in vivo. Elderly clinically tumor-free C3H mice showed measurable NK activity, which dropped after the appearance of spontaneous mammary tumors to very low levels, the magnitude of decline rising with increasing tumor age (1-11 weeks) or size. The incidence of NK lineage cells was measured from the tumor target (YAC-1 lymphoma)-binding ability of the splenic null cells, identified with a radioautographic technique. Null target-binding cells (TBC) were NK-1+ and included both active as well as inactive NK lineage cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of erythroid colony progenitors in a subset of human peripheral null lymphocytes devoid of Fc receptors

This study was aimed at purifying the progenitors of erythroid burst units (BFU-E) from human peripheral blood. Human mononuclear leukocytes from five normal donors were fractionated into several mononuclear cell subpopulations, including null lymphocytes with (null Fc+) and without (null Fc-) receptor for the Fc fragment of immunoglobulin G, through a succession of rosetting procedures and discontinuous Ficoll-Hypaque gradient centrifugations. The fractionated cells were separately cultured for 14 days in plasma clots in the presence of erythropoietin. Among fractionated cell subpopulations large and numerous BFU-E derived colonies grew only from the Fc- null lymphocyte subpopulation. This fraction, representing less than 4% of all mononuclear cells, also contains cells (42 + 11%) capable to differentiation towards the B-cell and plasma-cell lineages. The Fc+ null lymphocytes, representing less than 9% of all mononuclear cells, contained 15.2 + 3.3% cells capable of differentiation toward the T-cell lineage. The whole null lymphocyte subpopulation generated half the number of BFU-E colonies expected from its content in Fc- null lymphocytes. These data demonstrate that the progenitor of erythroid cells (BFU-E) resides in a small heterogeneous null Fc- subpopulation of circulating lymphocytes and suggest that its in vitro differentiation, though generally subjected to inhibitory and enhancing influences from other circulating cell subpopulations, does not necessarily require interaction with other peripheral blood cells.