Demonstration of C3 receptors on frozen sections of normal lymphoid tissue and malignant lymphomas using various EAC complexes

Summary The occurrence and distribution of complement receptors (C3R) were investigated on frozen sections from normal lymphoid tissue and from 185 cases of malignant lymphoma. Various EAC complexes were used: vital EA or glutaraldehyde-fixed EA coated with mouse complement (EAC mouse and Glu-EAC mouse, respectively), human complement (EAC human and Glu-EAC human), or complement from C6-deficient rabbits (EAC_ra-C6-def, Glu-EAC_ra-C6-def). The different EAC complexes showed varying affinity for C3R: Glu-EAC human > EAC mouse = EAC_ra-C6-def > Glu-EAC mouse = Glu-EAC_ra-C6-def > EAC human. The EAC complexes differed not only in their receptor affinity but also in their pattern of binding. On frozen sections of tonsils, EAC mouse, EAC human and EAC_ra-C6-def adhered exclusively to germinal centers and the follicular mantle, whereas Glu-EAC mouse, Glu-EAC human and Glu-EAC_ra-C6-def adhered not only to germinal centers and the follicular mantle but also to parafollicular areas and sometimes to interfollicular regions. The various EAC complexes were also assayed for reactivity to C3b receptors of human erythrocytes and C3R of human tonsil cells. Human erythrocytes (C3b receptor⁺ and C3d receptor^– did not react with EAC mouse, EAC human or EAC_ra-C6-def whereas tonsil cells (C3b and C3d receptor⁺) showed positive reactions with these complexes. In contrast, Glu-EAC mouse, Glu-EAC human and Glu-EAC_ra-C6-def displayed marked affinity for both the C3b receptors of human erythrocytes and the C3Rof tonsil cells. In connection with previously reported data, these findings indicate that (a) EAC mouse, EAC human and EAC_ra-C6-def react only with receptors for C3d, whereas Glu-EAC human, Glu-EAC mouse and Glu-EAC_ra-C6-def are bound by C3b receptors and probably by C3d receptors as well, and (b) germinal center cells and follicular mantle lymphocytes express C3b and C3d receptors whereas cells in parafollicular areas and those in the interfollicular zone bear only C3b receptors.On frozen sections from a fetal thymus C3R could be clearly demonstrated with Glu-EAC human. The demonstration of C3R on frozen sections from malignant lymphomas with the Glu-EAC human complex revealed C3R on cells from all types of lymphoma except mycosis fungoides, although there were variations in the number of positive cells and in the density of the reaction. C3R were most common and were expressed most densely in two types of germinal center cell tumors, viz. centroblastic/centrocytic lymphoma and centrocytic lymphoma. Combined with the investigation of acid phosphatase activity and the sheep erythrocyte rosette test, analysis of C3R in lymphoblastic lymphomas of the T type led to the distinction of three subtypes, viz. a prethymocytic, a prothymocytic, and a mature thymocytic subtype. In none of the cases of Hodgkin's disease tested could C3R be demonstrated unequivocally on Hodgkin or Sternberg-Reed cells.This study was supported by the Deutsche Forschungsgemeinschaft SFB 111, Project CL1     

Absence of terminal transferase may predict failure of remission induction in childhood ALL

Two children with acute lymphoblastic leukemia (ALL), whose lymphoblasts lacked terminal deoxynucleotidyl transferase (TdT) by both enzyme and fluorescent antibody assay, responded poorly or not at all to vincristine and prednisone. Both patients had high presenting white counts and mixed L1-L2 morphology. Lymphoblasts from one patient, an adolescent boy with a mediastinal mass, possessed surface membrane receptors for sheep red cells (E) and for complement (EAC) and had elevated adenosine deaminase activity (ADA). Lymphoblasts from a 2.5-yr- old boy without a mediastinal mass did not form E or EAC rosettes and did not express the la-like antigen or carry surface immunoglobulin. The poor response to therapy and absence of TdT were associated with a lymphoblast phenotype suggestive of a highly differentiated T-cell- derived line in one instance and an undifferentiated cell in the other instance. It is postulated that absence of TdT may predict poor therapeutic efficacy of vincristine and prednisone in acute lymphoblastic leukemia in childhood. The absence of TdT may correlate with other developmental characteristics of lymphoblasts, such as altered function or low numbers of glucocorticoid receptors or resistance to lysis by steroid drugs. Determination of many parameters of lymphoblast phenotype at diagnosis to characterize the nature of the malignant cells more precisely may ultimately enhance our understanding of, and improve therapy for, the group of leukemic children who fail to respond to standard regimens.     

Lymphocyte Membrane Markers in Acute Lymphoblastic Leukaemia

S ummary . T and B lymphocytes can be detected by specific membrane markers. Spontaneous rosette formation with sheep RBC (E rosette) is a T cell marker, whereas receptors for activated complement component (EAC), for the Fc regions of certain immunoglobulin classes (FcR), and for membrane immunoglobulins (mIg) are specific for B cells. Using these lymphocyte membrane markers we evaluated peripheral blood lymphocytes of 18 patients in different stages of acute lymphoblastic leukacmia (ALL).
Our results indicate that in acute untreated ALL there is no set immunologic pattern; instead there is a variety of selective deficiencies. Patients in remission have normal populations of T and B cells, whereas those in relapse present a rather obscure picture.
The percentage of lymphocytes with membrane markers was compared to the percentage of blast cells and an inverse relation is observed. This indicates that these are abnormal blast cells.
The changes from the untreated acute stage through to remission was followed in one subject, and in two others additional study was performed on bone marrow and spinal fluid lymphocytes.     

Prolymphocytic leukaemia: surface morphology in 21 cases as seen by scanning electron microscopy and comparison with B-type CLL and CLL in ''prolymphocytoid'' transformation

The surface architecture of leukaemic cells obtained from 21 cases of proven prolymphocytic leukaemia (PLL) and eight cases of chronic lymphocytic leukaemia (CLL) with 'prolymphocytoid' transformation (PL-CLL) was compared with the cell surface morphology of leukaemic cells obtained from 46 cases of B-type CLL, using the scanning electron microscope (SEM). All cases were defined by cytochemistry, immunological markers and transmission electron microscopy prior to SEM examination. B-CLL cells showed the well-recognized spectrum of surface architecture described in earlier studies. The majority of cells had moderate numbers of short microvilli, although in a minority, cells with relatively smooth surfaces predominated. In seven of the eight cases of PL-CLL, cells were villous in nature and in this respect similar to CLL cells; however, more cells with dense microvilli were seen. The prolymphocytic cells were recognized by their larger size and in 18 of the 19 cases of B-derived PLL, villous cells predominated. Two cases of T-derived PLL showed variable cell surface morphology ranging from smooth to moderately villous. It appears that B-PLL cells are most frequently villous and display more surface microvilli than B-CLL cells. B-prolymphocytes display the surface features regarded as characteristic for neoplastic B-cells as seen in patients with B-type lymphoma and leukaemia.     

Significance of the determination of red cell enzyme activities.

Normal human peripheral blood cells were separated into different populations based upon isopycnic sedimentation, E rosetting, and EAC rosetting. Each population was characterized according to morphology, surface markers, granulocytic colony formation in semi-solid media, and stainable RNA content by acridine orange (AO) flow cytometry. These techniques enrich for a population of cells that is characterized by a lymphoid morphology, a high granulocytic-macrophage progenitor cell cloning efficiency, a lack of surface markers, and a high stainable RNA content not found in the other two populations of peripheral blood lymphocytes (T cells and B cells). The stainable RNA content serves as a new metabolic marker for the population of cells in which the preponderance of granulocytic progenitor cells reside.     

Characterization of lymphoblast Fc receptor expression in acute lymphoblastic leukemia.

Lymphoblasts from 18 patients with untreated acute lymphoblastic leukemia were investigated for the presence of conventional cell surface markers (spontaneous sheep red blood cell rosette formation, complement receptors, and surface immunoglobulin). The expression of Fc receptors for both IgG and IgM was investigated using indicator bovine erythrocytes coated with rabbit anti-BRBC (IgG and LgM fractions). The leukemic cells of all patients in this tudy expressed Fc receptors for both IgC and LgM. In contrast with previous reports, null (non-T non-B) lymphoblasts as well as T lymphoblasts demonstrated Fc-IgG and Fc-IgM receptors. However, these two immunologic subclasses of leukemic cells demonstrated significantly different patterns of Fc receptor distribution. These data suggest that expression of Fc receptors is an early event in cellular differentiation in this lymphoid malignancy.     

Morphological Differences between Sub-Populations of Human Lymphocytes Revealed by Scanning Electron Microscopy

Human lymphoid cells were examined by scanning electron microscopy (SEM) to see if a correlation existed between surface morphologic features and the presence of various surface markers and receptors. When viewed by SEM thymocytes appeared as smooth-surfaced cells with few surface microvilli; peripheral blood lymphocytes (PBL) on the other hand were moderately to densely villate with no entirely smooth-surfaced cells observed. Surface morphology within PBL samples was not uniform, due mainly to variations in the shape and number of microvilli. However, 2 distinctive types of surface morphology (termed Types 1 and 2) were discernable with a small number of cells displaying features of both groups (Type 3). The majority of E-rosette forming cells (T lymphocytes) displayed Type 1 and the majority of cells bearing demonstrable surface immunoglobulin (B lymphocytes) displayed Type 2 morphology. Exposure of PBL to anti-T cell specific ALG resulted in cytolysis of cells with Type 1 morphology while cells with Type 2 morphology appeared largely unaffected. PBL with Fc and C₃ receptors displayed all 3 types of morphology. It is concluded that T and B lymphocytes do have subtle but nevertheless discernable differences in surface morphology and within these 2 groups, variations in surface morphology are probably associated with changes in the physiological status of the cell.     

Morphological differences between sub-populations of human lymphocytes revealed by scanning electron microscopy.

Human lymphoid cells were examined by scanning electron microscopy (SEM) to see if a correlation existed between surface morphologic features and the presence of various surface markers and receptors. When viewed by SEM thymocytes appeared as smooth-surfaced cells with few surface microvilli; peripheral blood lymphocytes (PBL) on the other hand were moderately to densely villate with no entirely smooth-surfaced cells observed. Surface morphology within PBL samples was not uniform, due mainly to variations in the shape and number of microvilli. However, 2 distinctive types of surface morphology (termed Types 1 and 2) were discernable with a small number of cells displaying features of both groups (Type 3). The majority of E-rosette forming cells (T lymphocytes) displayed Type 1 and the majority of cells bearing demonstrable surface immunoglobulin (B lymphocytes) displayed Type 2 morphology. Exposure of PBL to anti-T cell specific ALG resulted in cytolysis of cells with Type 1 morphology while cells with Type 2 morphology appeared largely unaffected. PBL with Fc and C3 receptors displayed all 3 types of morphology. It is concluded that T and B lymphocytes do have subtle but nevertheless discernable differences in surface morphology and within these 2 groups, variations in surface morphology are probably associated with changes in the physiological status of the cell.     

Isolation and characterization of infiltrates in the nerves of patients with neuritic leprosy

A study was done on the characteristics of infiltrating cells in the nerves of 9 patients with pure neuritic leprosy, by preparing a single cell suspension. The patients had no skin lesion. Histopathological examination revealed that 2 of the 9 nerves showed granulomas characteristics of tuberculoid leprosy, while the remaining 7 had features of lepromatous granulomas. In the nerves showing tuberculoid granulomas, a high proportion of lymphocytes were T cells as they formed rosettes with sheep erythrocytes and only a few percent were EAC rosette forming cells. On the other hand, the nerves showing lepromatous granulomas contained only occasional lymphocytes which formed E and EAC rosettes. Macrophages from the granulomas of all the nerves were esterase positive, peroxidase negative, contained M. leprae and did not exhibit C3 surface receptors.     

C3d receptors are expressed on human monocytes after in vitro cultivation.

Highly purified human third component of complement (C3) was used to coat sheep erythrocytes (E) that were sensitized with IgM antibody (EA), forming EAC3b over a wide range of C3 molecules per cell. EAC3b were converted to EAC3bi by incubation with purified C3b inactivator (factor I) and beta 1H globulin (factor H). EAC3bi were in turn trypsinized to produce the cellular intermediate EAC3d. Each of the cell types was carefully characterized to be certain of the type of C3 determinant expressed. These cellular complement intermediates were used to assess by rosette formation the C3 receptor activity on peripheral blood monocytes under various experimental conditions. Uncultivated monocytes from peripheral blood bound EAC3b and EAC3bi well but did not bind EAC3d significantly. However, upon cultivation on glass surfaces in the presence of fetal calf serum but not bovine serum albumin, monocytes showed a progressive increase in expression of the C3d receptor. The Fab' fragment of anti-C3c blocked binding of EAC3b completely, blocked EAC3bi partially, but failed to block binding of EAC3d to cultivated monocytes. In contrast, the Fab' fragment of anti-C3d blocked EAC3d rosette formation completely. These studies demonstrate that monocytes are capable of expressing receptor activity for a determinant on C3d but that the expression of this receptor depends on the state of activation or differentiation of the cells.     

Surface characteristics of synovial fluid and peripheral blood lymphocytes in inflammatory arthritis

In order to characterize the T- and B-cell populations of inflammatory arthritides, synovial fluid and peripheral blood lymphocytes from patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), juvenile rheumatoid arthritis (JRA), and rheumatoid variant diseases (RV) were studied. Normal peripheral blood lymphocytes were examined as controls. T cells were identified by spontaneous sheep red blood cell (E) rosette formation. B cells were determined by complement receptor lymphocyte (EAC) rosette formation and by the presence of surface immunoglobulins (SIg) utilizing fluoresceinated polyvalent antiglobulin. Synovial fluids were analyzed in terms of duration, mucin quality, white cell count, and differential. Synovial fluid and peripheral blood lymphocytes from patients with RA and RV were distributed in T- and B-cell percentages similar to those found in normal peripheral blood. In contrast, significant T-cell depression was observed in the percentage of synovial fluid and peripheral blood lymphocytes of SLE and JRA patients. This depression was apparent in comparison with normal peripheral blood and with the synovial fluid and peripheral blood from RA patients. B-cell percentages were similar in all patient groups and in comparison to normal peripheral blood lymphocytes. No differences were noted in B-cell percentages when the EAC and SIg techniques of identification were compared. The percentage of cells bearing neither T- nor B-cell markers (null cells) was enumerated for each patient group and found to be significantly elevated in the synovial fluid and peripheral blood of SLE and JRA patients. Though the mean synovial fluid and peripheral blood null cell percentages in RA patients were similar to those in controls, a definite bimodal distribution was found in the synovial fluids. These data suggest that evaluation of T-, B-, and null-cell populations may be clinically useful in differentiating patients with SLE and JRA from those with rheumatoid arthritis and variant diseases.     

Complement receptors in atherosclerotic lesions.

Accumulation of cholesterol in the tunica intima of arteries is a feature of atherosclerotic development. Recently, the demonstration of oxidized LDL in atherosclerotic lesions considerably strengthened the possibility of its role in the atherogenesis in vivo. However, the mechanism of lipid accumulation in monocyte-derived macrophages has not yet been clarified. It has been reported that the complement system may be related to atherosclerosis. In this report, complement receptors in the atherosclerotic lesions obtained from autopsy sample were investigated. Initially C3b receptors were detected using sheep erythrocytes bearing human C3b (EAC1423b cells). EAC1423b cells adherent to only aortic sections showing intimal thickening, but not to intact artery. Second, immunostaining of consecutive aortic sections was performed. Apo B and C5b-9 complex were stained using the indirect immunoperoxidase method, and macrophage, C3b receptor (CR1) and C3bi receptor (CR3) were stained using monoclonal antibody in the alkaliphosphatase anti-alkaliphosphatase method. In the intact artery of 3 month old patient, antigen- specific staining were not observed. In intimal thickening and atheroma of older patients, consecutive sections suggested that complement receptor-expressing cells were macrophages. Staining for apo B antigen existed at extracellular site in the intima, and C5b-9 complex was observed in intima and partially in the media. The above data showed that macrophage complement receptors were expressed in the atherosclerotic lesions when the complement system was activated. We conclude that these data suggest that the complement system and complement receptors may be related to the uptake of LDL by macrophages.     

The inhibitory effect of ionizing radiation on Fc and C3 receptors on mouse and human leukocytes, and the protective potential of human albumin

The effect that ionizing radiation has in vitro on Fc and C3 receptors was evaluated at various doses and measured by means of erythrocytes coated with antibody (EA) and erythrocytes coated with antibody and complement (EAC) rosettes on human peripheral blood leukocytes (PBL) and on mouse bone marrow cells (BMC) and PBL. We found that the number of cells with either EA and EAC rosettes decreased as the radiation doses increased, and that they were almost absent when the highest doses were employed. We obtained evidence that albumin is a natural source of radio-protection for Fc and C3 receptors, and we showed that by increasing the amount of this molecule we could completely protect receptors for EA and EAC in vitro. Finally, the possible therapeutic value of the administration of human albumin to patients undergoing radiotherapy is discussed.     

Prognostic significance of surface marker analysis in childhood non-hodgkin's lymphoproliferative malignancies

Blast cell surface markers for T- and B-lymphocyte characteristics were studied at diagnosis in 73 children with non-Hodgkin's lymphoproliferative malignancies. Three distinctive groups of patients were identified on the basis of the analysis of blast cells for surface immunoglobulin (SIg), sheep erythrocyte (sE) rosette formation, and complement receptors. The seven group I patients had monoclonal IgM on their blast cells, morphologic features of Burkitt's lymphoma, abdominal masses, and very short survival. The 13 group II patients had receptors for sE, complement, or both on their blast cells, mediastinal or nodal masses, and short survival. The distinction between leukemia and lymphoma based on the presence of bone marrow involvement at diagnosis is not prognostically useful in this group of patients. The blast cells of group II patients could not be morphologically distinguished from those of the group III patients. The 53 group III patients had SIg, sE, and complement negative blast cells and could be further subdivided on the basis of white blood cell count. The nine group III_A patients (> 100.0 × 10⁹/liter) had in general short survival, while most of the 44 group III_B patients (< 100.0 × 10⁹/liter) have remained in complete remission. Positive surface markers, mass lesions, male sex, and age of diagnosis < 2 years or ≧ 10 years appear to be interrelated factors indicating poor prognosis. Elevated white blood cell count is a prognostic indicator independent of surface marker analysis or presence of mass lesions.     

Hodgkin's disease: Establishment and characterization of four in vitro cell lines

Summary Four in vitro cell lines (L 428, L 439, L 538, and L 540) were established from different materials of three patients with Hodgkin's disease: pleural effusions, peripheral blood, and bone marrow. The histological diagnosis was confirmed in all cases by several independent histologists. All four cell lines have been in culture for over 6 months up to over 3 years. The neoplastic nature of the culture cells is indicated by the demonstration of several structural and numeric chromosome abnormalities associated with a monoclonal pattern of marker chromosomes. EBV-specific antigens (EBNA, VCA) were not detected in either cell line. Ia-like antigens, receptors for human T cells, acid phosphatase, and acid esterase were shown to be present in the cultured cells. All cell lines lacked surface or cytoplasmic Ig, HTLA, receptors for C3b, C3d, IgG-Fc, mouse E or sheep E, and were devoid of lysozyme, peroxidase, and chloracetate esterase. The described features do not represent B cells, T cells, myeloid cells, monocytes, or macrophages. The morphology and the marker pattern of the culture cells, however, is identical with that of freshly obtained Hodgkin's (H)- and Sternberg-Reed (SR)-cells, except for the lack of CIg in the in vitro cells, which is explained by the culture conditions. Heterotransplantation in nude mice was achieved by intracranial inoculation and by s.c. transplantation of cultured cells embedded in a plasma clot. The described findings suggest that these cultured Hodgkin's cell lines are indeed derived from H and SR cells. The cellular origin of these cells is not clear, the loss of cellular differential markers during the process of possible dedifferentiation is discussed.Supported by the Deutsche Forschungsgemeinschaft Bonn/Bad Godesberg, grant nos. Di 184/6 and SFB 111/D8     

Evidence for the presence of receptors for c3 and IgG Fc on human synovial cells

The presence of receptors for IgG Fc and fragments of C3 on primary cultures and cryostat sections of normal and rheumatoid synovial tissues was assessed. Significant proportions of large rounded cells with asteroid projections found in such cultures had receptors for both IgG Fc and fragments of C3. Moreover, Gram negative bacteria that had fixed complement, but not EAC, bound in a linear fashion on the superficial layers of synovial cryostat sections. On the basis of morphologic and histochemical criteria, the cultured cells bearing these receptors were tentatively determined to represent a subset of synovial lining cells. The possible role of such receptors on synovial lining cells in the pathogenesis of rheumatoid arthritis is discussed.     

LYMPHOPENIA AND CHANGE IN DISTRIBUTION OF HUMAN B AND T LYMPHOCYTES IN PERIPHERAL BLOOD INDUCED BY IRRADIATION FOR MAMMARY CARCINOMA

Irradiation for mammary carcinoma frequently leads to a lymphopenia lasting for at least a year. An analysis of the relative proportion of bone-marrow (B) and thymus (T) dependent lymphocytes in peripheral blood has been done in these patients. One surface marker characteristic for B lymphocytes (receptors for activated complement, EAC) and spontaneous rosette-forming capacity for sheep red blood-cells (E), a property of human T lymphocytes, have been investigated in peripheral-blood lymphocytes up to a year after radiotherapy. The ability of lymphocytes to respond to the stimulus of phytohæmagglutinin (P.H.A.) was also tested before and after irradiation was given in vivo. Thirty-four patients have been followed up by blood differentials over a year and the frequency of B and T cells analysed. A statistically significant lymphopenia was found 1 year after unilateral parastemal irradiation. Healthy controls had a mean of 32% EAC-binding lymphocytes (B cells) and 60% E-binding lymphocytes (T cells). After irradiation there was a statistically significant shift in the proportion of EAC and E binding lymphocytes, with a decrease of T lymphocytes to 45% and a relative increase of B cells to 52%. The ability of lymphocytes to transform after in-vitro stimulation with P.H.A. was decreased in fifteen of nineteen patients tested. The data suggest that irradiation for mammary carcinoma leads to a long-lasting lymphopenia which mainly is a selective T-lymphocyte lymphopenia. These findings may be relevant for the development of distant metastases.     

Distribution of complement receptor subtypes in non-Hodgkin's lymphomas of B-cell origin

Surface receptors specific for either the C4b (CR1) or C3d (CR2) component of complement were examined on the neoplastic cells from 30 cases of non-Hodgkin's lymphoma of B-cell origin and on cells derived from 9 normal lymphoid tissues. Lymphocyte suspensions from non- neoplastic peripheral blood, tonsils, and lymph node contained three categories of complement receptor lymphocytes (CRL): cells with receptors for both C4b and C3d (CR1+, CR2+); cells with receptors for C4b but not C3d (CR1+, CR2-), and cells with receptors for C3d but not C4b (CR1-, CR2+). The mean of the proportion of total CRL expressing receptors only of C3d (CR1-, CR2+) was 0.35 for non-neoplastic tissues and 0.28 for malignant lymphomas of follicular center cell (FCC) origin. However, the proportion of cells with this phenotype was significantly higher in well differentiated lymphocytic lymphomas (WDL) and chronic lymphocytic leukemia (CLL) (0.65) and in intermediately differentiated lymphocytic lymphomas (IDL) (0.59). Histologic compartmentalization of the CRL subtypes was observed in frozen sections of normal lymphoid tissue. CR1+ cells were present in lymphoid follicles interfollicular areas, and in splenic red pulp. CR2+ cells were confined to lymphoid follicles. These findings strongly suggest that complement receptor phenotypes may be useful markers of B-cell differentiation.     

Cell markers in hairy cell leukemia studied in cells from 51 patients

To determine the maturation arrest of the neoplastic cells of hairy- cell leukemia (HCL) and the spectrum of the surface markers on these cells, a series of 51 patients with this disease was studied. The cells of all but two of the patients showed monoclonal surface Ig with respect to light chains. In about one-third of the cases, only gamma heavy chain determinants were present on the cells; the majority carried multiple heavy chain determinants as documented by the application of different fluorochromes. Two patients each showed two different clones of cells, both of the same light chain type. In one of these two patients, two paraproteins were present in the serum. Intracytoplasmic Ig was found in only 4 of 39 cases, in all instances being IgM. All cases studied concerned cells with FclgG receptors; however, the density of this receptor varied. FcIgM receptors also showed a spectrum of density, with some cases showing very few FcIgM- positive cells. Receptors C3 were not observed on the hairy cells. Serum immunoglobulin levels were normal or increased. Paraproteins were found in the sera of 4 of 38 patients. These data suggest that HCL is a neoplasm of B lymphocytes. The neoplastic cells are probably arrested at a more mature stage than the cells of chronic lymphocytic leukemia. The multiple isotypes on the cells indicate a block at the "switch" phase from the small micro-carrying lymphocyte to the larger Ig- producing lymphocyte or plasma cell.     

Lymphocytic thymoma associated with T-cell lymphocytosis.

A 64 year old woman presented with lymphocytosis and an interior mediastinal mass, but without lymphadenopathy, hepatosplenomegaly or skin lesions. T-cell surface markers (rosette formation with sheep erythrocytes and reactivity with antithymocyte antiserum) could be demonstrated on lymphocytes from the blood, mediastinal tumor and pleural fluid; B-cell markers (surface immunoglobulin and complement receptors) were absent. The clinical and pathologic features in this case were quite different from those of known leukemias of small mature T lymphocytes, i.e., the Sézary syndrome of mycosis fungoides and T-cell chronic lymphocytic leukemia. It is concluded that this case represents the second example of a new proliferation of mature T cells, lymphocyte predominant thymoma with lymphocytosis.