Interleukin 1 as an autocrine growth factor for acute myeloid leukemia cells

Production of interleukin 1 (IL-1) by leukemic cells was studied in 13 cases of acute myeloid leukemia. Intracytoplasmic immunofluorescence studies showed that the cells invariably contained the cytokine. Endogenous labeling studies demonstrated that acute myeloid leukemia cells produced either only the 33-kDa propeptide or both the propeptide and the 17-kDa mature form of IL-1 beta. The 33-kDa propeptide IL-1 alpha was always produced but was less frequently released. Involvement of IL-1 in leukemic cell growth was investigated using two antibodies specific for IL-1 subtypes, which inhibited spontaneous cell proliferation in the six cases studied. After acid treatment of the cells, a surface receptor for IL-1 could be demonstrated, which mediated 125I-labeled IL-1-specific uptake by leukemic cells. Furthermore, recombinant IL-1 alpha or IL-1 beta induced significant cell proliferation in 10 of 12 cases. The above findings were uncorrelated with the cytologic type (French-American-British classification) of leukemia. Our studies suggest that IL-1 may act as an autocrine growth factor in most cases of acute myeloid leukemia.

Regulation of IgM biosynthesis in human chronic lymphocytic leukemia. Normal and neoplastic B cells respond differently to TPA

According to the pattern of IgM biosynthesis (membrane expression and secretion), human B cell chronic lymphocytic leukemias (B-CLLs) were subgrouped into four classes, namely: class I: membrane- secretion-; class II: membrane+ secretion-; class III: membrane+ secretion+; class IV: membrane- secretion+. Abundant membrane mu chain mRNA was present in cells from all cases, indicating that translational and/or post translational events were responsible for the absence of surface IgM in classes I and IV. Similarly, post translational events blocked IgM secretion in non secreting B-CLL cells. In B-CLLs from classes I, II and III, TPA induced IgM secretion by up-regulating secretory mu chain mRNA. By contrast, in normal B cells, TPA induced down-regulation of the secretory form of Ig mRNA, irrespective of the maturational stage of the cell. These observations indicate that IgM biosynthesis is modulated differently by TPA in normal and malignant B cells.

Immunoglobulin heavy-chain switching may be directed by prior induction of transcripts from constant-region genes

Immunoglobulin heavy-chain switching is effected by a DNA recombination event that replaces the C mu gene with one of the other heavy-chain constant-region (CH) genes located 3' to the C mu gene. How the specificity of this event is controlled is unknown. However, it has been shown that IgM+ cells capable of switching to specific isotypes have the corresponding unrearranged CH genes in an accessible or active chromatin state, as demonstrated by the fact that these specific CH genes are hypomethylated and are transcriptionally active. We now report that the RNAs transcribed from specific unrearranged CH genes are induced prior to switching under conditions that promote switching to these specific CH genes. For example, we find that bacterial lipopolysaccharide, which induces the IgM+ cell line I.29 mu to switch to IgA, induces transcripts from the germ-line C alpha gene(s) in I.29 mu cells prior to switch recombination. Two preparations of T-cell lymphokines (recombinant interleukin 4 and supernatant from the T-cell line 2.19, which contains interleukins 4 and 5) that promote switching to specific isotypes by lipopolysaccharide-treated spleen cells induce transcripts from the corresponding germ-line CH genes prior to expression of the new isotypes. For example, interleukin 4, which appears to be necessary for switching to IgE in vitro and in vivo, induces within 2 days large increases in germ-line C epsilon transcripts in lipopolysaccharide-treated spleen cells and in I.29 mu cells. The most straightforward interpretation of our data is that these lymphokines direct switching to specific isotypes by activating specific CH genes, making them accessible to the putative switch recombinase.

The control of membrane and secreted heavy chain biosynthesis varies in different immunoglobulin isotypes produced by a monoclonal B cell lymphoma

The control of production of the membrane (m) vs secreted (s) forms of immunoglobulin heavy chains was investigated in a panel of cell lines expressing different heavy chain classes but identical light chains (lambda) and variable regions. These cell lines could be induced towards Ig secretion by mitogen treatment. During this process a shift from m to s heavy chain production takes place. Here we show that, similarly to IgA- and IgE-producing B cells, in IgG2a-producing I.29 cells the gamma m-gamma s shift was accompanied by a shift in the corresponding mRNAs, with a decrease of gamma m mRNA and an increase of the gamma s mRNA in LPS-stimulated cells. By contrast, the micron mRNA was increased in LPS-stimulated IgM-producing cells, albeit these cells synthesized reduced amounts of micron polypeptides. The utilization of the translational level in the early steps of B lymphocyte maturation thus distinguishes the mode of regulation of mu chains from those of the other isotypes. In addition, in B cells a post-translational event blocks the secretion of IgM but not of IgG or IgE.

Regulation of membrane IgM expression in secretory B cells: translational and post-translational events

IgM secreting cells express little or no membrane IgM. This is not always due to absence of the relevant mRNA. To investigate the synthesis and processing of membrane (micron) and secreted (microseconds) polypeptides in secretory B cells, myeloma cells were transfected either with a plasmid containing an intact mu gene or with one only capable of directing micron (not microseconds) mRNA synthesis. Although myeloma transfectants could make abundant levels of micron mRNA, they did not express IgM on the cell surface. In the myeloma host, micron mRNA is translated some 5-fold less efficiently than microseconds mRNA. However, this translational control does not totally preclude micron synthesis, indicating post-translational regulatory events. No difference between micron and microseconds chains could be detected in their rate of assembly with light chains or in their stability, although both types of heavy chain were degraded more rapidly when synthesized in the absence of light chain, or when the hydrophobic nature of the leader sequence was destroyed by site-directed mutagenesis. However, whereas intracellular microseconds chains in IgM-secreting plasmacytoma were found to be concentrated in the Golgi, the micron chains were mainly located in the endoplasmic reticulum. Retention in the endoplasmic reticulum is also observed for both micron and microseconds when synthesized in the absence of light chain. We propose that it is the expansion of the endoplasmic reticulum that accompanies B cell to plasma cell differentiation which is in part responsible for the down-regulation of surface IgM expression. Such a mechanism may also affect the expression of other surface proteins.

Differentiation in the murine B cell lymphoma I.29: individual mu + clones may be induced by lipopolysaccharide to both IgM secretion and isotype switching

Cells from the monoclonal B cell lymphoma I.29 expressing surface IgM (mu +) are capable of differentiating in vitro to IgM secretion and of switching to IgA or IgE production in response to lipopolysaccharide (LPS) stimulation. To determine whether a single mu + B cell is capable of undertaking both differentiative pathways (isotype switch and plasma cell differentiation) I.29 mu + cells were cloned by limiting dilution and a panel of clones were analyzed by immunofluorescence, endogenous labeling and Northern blotting. While 100% of the clones could differentiate toward IgM secretion, only a proportion of them (greater than 70%) also switched to IgA and/or IgE production. Certain clones switched preferentially to a specific isotype. Taken together with the observation that C gamma genes were never the target of switching in our experiments, these data suggest that individual mu + clones from the I.29 lymphoma are "precommitted" as for their switching potentials. The subclones that showed a high frequency of switching to IgA transcribed the germ line C alpha gene(s), suggesting a role for chromatin structure in determining the isotype switch specificity. Switch variant clones expressing either IgA or IgE on the cell surface were isolated and found capable of further differentiating toward Ig secretion in response to LPS. On the contrary, we could not induce switch to IgA in IgE-producing cells. Unlike mu + and alpha + cells, all the switch variant clones expressing IgE tested by endogenous labeling constitutively secreted large amounts of IgE in the supernatants even in the absence of LPS stimulation.

Biosynthesis of membrane and secreted epsilon-chains during lipopolysaccharide-induced differentiation of an IgE+ murine B-lymphoma

A switch variant of the I.29 murine B-cell lymphoma expressing membrane IgE and inducible by lipopolysaccharide (LPS) to increase the rate of IgE secretion was characterized. The cells (I.29 epsilon +2) express membrane-bound IgE, and also secrete considerable amounts of IgE when grown in regular culture medium. Membrane and secreted IgE contain structurally different heavy chains. The former is constituted by a 93-kd molecule (epsilon m), while secretory chains (epsilon s) have an apparent mol. wt of 86,000. Both epsilon m and epsilon s are heavily glycosylated: in the presence of tunicamycin their apparent mol. wt is reduced by approx. 35% (61 kd for epsilon m and 56 kd for epsilon s). Glycosylation is necessary for membrane expression and for secretion of IgE molecules. Stimulation with LPS leads to the disappearance of IgE molecules from the cell surface (determined by radioiodination) although epsilon m-chains are still synthesized, suggesting a defective transport of membrane IgE in LPS-treated cells. The epsilon m:epsilon s ratio decreases upon LPS stimulation. A similar change can be observed in the messenger RNAs specific for epsilon m and epsilon s, possibly suggesting a major pretranslational control for epsilon m and epsilon s biosynthesis.

The regulation of membrane-bound and secreted alpha-chain biosynthesis during the differentiation of the B cell lymphoma I.29

The regulation of the synthesis of membrane-bound and secreted IgA was investigated in the murine B lymphoma I.29 during the differentiation from IgA-bearing lymphocytes to IgA-secreting cells, as caused by treatment with lipopolysaccharide (LPS). LPS induced a threefold to fivefold increase in the amount of IgA synthesized, and induced a shift from the synthesis of the membrane form of alpha-chain (alpha m) to the synthesis of the secreted form of alpha-chain (alpha s), resulting in a 60-fold increase in the amount of IgA secreted. In vitro translation of sucrose gradient-fractionated RNA indicated that two mRNA molecules, 3.1 and 2.1 kilobase pairs (kb), encode alpha m-chains, whereas a smaller RNA molecule, 1.7 kb, encodes alpha s. Analyses by RNA blotting showed that the relative amounts of the three alpha mRNA changed rapidly during LPS-induced differentiation. The amount of the 3.1 and 2.1 kb alpha mRNA decreased, and the amount of the 1.7 kb alpha s mRNA increased in LPS-stimulated cells as compared with controls. These observations suggest that the regulation of alpha m/alpha s synthesis is controlled mostly at the pretranslational level.

The regulation of membrane-bound and secreted alpha-chain biosynthesis during the differentiation of the B cell lymphoma I.29

The regulation of the synthesis of membrane-bound and secreted IgA was investigated in the murine B lymphoma I.29 during the differentiation from IgA-bearing lymphocytes to IgA-secreting cells, as caused by treatment with lipopolysaccharide (LPS). LPS induced a threefold to fivefold increase in the amount of IgA synthesized, and induced a shift from the synthesis of the membrane form of alpha-chain (alpha m) to the synthesis of the secreted form of alpha-chain (alpha s), resulting in a 60-fold increase in the amount of IgA secreted. In vitro translation of sucrose gradient-fractionated RNA indicated that two mRNA molecules, 3.1 and 2.1 kilobase pairs (kb), encode alpha m-chains, whereas a smaller RNA molecule, 1.7 kb, encodes alpha s. Analyses by RNA blotting showed that the relative amounts of the three alpha mRNA changed rapidly during LPS-induced differentiation. The amount of the 3.1 and 2.1 kb alpha mRNA decreased, and the amount of the 1.7 kb alpha s mRNA increased in LPS-stimulated cells as compared with controls. These observations suggest that the regulation of alpha m/alpha s synthesis is controlled mostly at the pretranslational level.

Differentiation in the murine B cell lymphoma I.29: inductive capacities of lipopolysaccharide and Mycoplasma fermentans products

Cells from the murine B lymphoma I.29, expressing IgM or IgA of identical idiotype, were found inducible by lipopolysaccharide to differentiate into plasma cells. Within 3 days, differentiating cells lost membrane-bound immunoglobulin (Ig) and accumulated large quantities of intracytoplasmic Ig. At day 6 of culture, IgA secretion increased 50-100-fold, as determined by enzyme-linked immunoassay. Proliferation increased for the first days of culture but decreased thereafter; by day 10 very few viable cells were present in lipopolysaccharide-stimulated cultures. Similar results were obtained by culturing I.29 cells in the presence of supernatants of certain B cell lines (e.g. BFO.3). The finding of a strict correlation between the inductive activity and presence of contaminating Mycoplasma fermentans suggested that factor(s) released by mycoplasma were responsible for the mitogenic activities. This was further indicated by the findings that: the supernatants of BFO.3 that were rendered free of mycoplasma were not inductive, and a nonactive cell line could be made active by infection with supernatants of BFO.3 cells containing viable microorganisms. Thus, supernatants of mycoplasma-infected cell lines may act as potent polyclonal activators on both normal and malignant B lymphocytes. The ability to induce membrane Ig on 70Z/3 cells indicates that mycoplasma-related mitogens are also active on pre-B cells. The possibility of mycoplasma contamination should thus be carefully excluded when presumptive factors of cloned cell lines are being evaluated.

Maturation of chronic lymphocytic leukemia B cells: correlation between the capacity of responding to T-cell factors in vitro and the stage of maturation reached in vivo

Circulating malignant cells from 15 patients with B-cell chronic lymphocytic leukemia (B-CLL) were examined by the electron microscope (EM) and tested for their capacity to produce immunoglobulin (Ig) molecules using endogenous labeling techniques in vitro. In agreement with previous observations, B-CLL clones from various patients could be subdivided in three distinct groups: immature (type 1) clones, that comprised mainly small resting lymphocytes which synthesized, but degraded Ig of the secretory type intracellularly; mature (type 3) clones consisting mainly of cells with an extended Golgi apparatus and numerous strands of rough endoplasmic reticulum (RER) that secreted Ig molecules; and clones (type 2) at an intermediate maturational stage. When stimulated with T-cell supernatants that contained T-cell replacing factor(s) (TRF), type 3 and, to a lesser extent, type 2 clones differentiated further and secreted increased amounts of Ig. This maturation was not observed when type 1 clones were stimulated with the same supernatants. However, these cells were not incapable of further maturation since they could differentiate in response to phorbol ester (TPA). The present data reinforce the concept that different CLL clones undergo a process of maturation in vivo that may be arrested at different levels and demonstrate that the various clones respond differently to physiological stimuli depending upon the level of maturation already reached in vivo.

The role of glycosylation in secretion and membrane expression of immunoglobulins M and A

The role of glycosylation in membrane expression and secretion of IgM and IgA was investigated in murine lymphoma and hybridoma cell lines, derived from I.29 tumor, which synthesize IgM or IgA with identical variable regions. Tunicamycin, a selective inhibitor of N-linked glycosylation, prevented the membrane expression of both isotypes, as demonstrated by immunofluorescence, radioiodination and endogenous labeling experiments. Selective immunoprecipitation and immunochemical analysis of membrane, intracellular and secreted molecules permitted us to determine the amount of membrane heavy chain externalized in the presence or absence of tunicamycin. Id 150 and Id 43, two I.29-derived hybridomas secreting IgA and IgM respectively, were differently affected by tunicamycin. While secretion of IgM was inhibited to greater than 95%, no inhibition of secretion of non-glycosylated IgA could be detected in Id 150 cells. These results indicate that different requirements for glycosylation exist in the biosynthetic pathways of immunoglobulin isotypes, and suggest that distinct intracellular transport systems may operate for membrane and secreted alpha-chains.

Differentiation of chronic lymphocytic leukemia cells: correlation between the synthesis and secretion of immunoglobulins and the ultrastructure of the malignant cells

The capacity of synthesizing and secreting Ig molecules was studied in 11 patients with B-cell chronic lymphocytic leukemia (B-CLL) whose cells expressed surface IgM, in 3 patients with surface IgG-bearing cells, and in 2 IgM prolymphocytic leukemias (IgM-PLL). Three types of mu chains were detected by SDS-polyacrylamide gel electrophoresis analysis of the endogenously labeled molecules isolated by specific immunoprecipitation. Two of them were isolated from the cell lysates and were identified as the membrane mu chain and the precursor of the secreted molecules, respectively. The latter also possibly contained precursors of the membrane molecules. The third type of molecule was detected only in the culture medium and was identified as secretory mu chain. Not all of the malignant clones possessed the three types of mu chains. Only 7/13 of the IgM-bearing malignant cell clones were capable of secretion, whereas the remaining synthesized the secretory mu chains but degraded them intracellularly. Two types of molecules (membrane and secreted) were found in the IgG-bearing CLL cells from three patients. In all of them, secretion was detected. Ultrastructural analysis demonstrated that cells from the secreting clones had the features of more mature lymphocytes than the cells from nonsecreting clones. These features were represented by a developed Golgi apparatus, various types of vesicles (smooth and coated), and strands of the rough endoplasmic reticulum. A certain heterogeneity of the degree of maturation of the cells was observed within these clones. The data are consistent with the hypothesis that CLL clones are heterogeneous and can be distinguished through the different degrees of maturation of their cell components.

Expression of a receptor for sheep erythrocytes by B lymphocytes from a chronic lymphocytic leukemia patient

A patient with a B-cell chronic lymphocytic leukemia, whose lymphocytes also formed rosettes with sheep red cells, is described. The B-cell nature of the malignant lymphocytes was determined by surface marker analysis, and cytochemical and ultrastructural studies. The lymphocyte membrane immunoglobulin (IgG1K) did not have anti-sheep red cell activity and was not responsible for the binding of sheep erythrocytes to the leukemic cells as shown by (i) the failure to inhibit rosette formation with anti-immunoglobulin reagents and (ii) the different sensitivity to proteolysis of the membrane immunoglobulin and the sheep erythrocyte receptor. The malignant lymphocytes expressed a receptor for sheep erythrocytes similar to that of normal T cells since they stained with monoclonal antibodies directed against the sheep red cell receptors. Furthermore these antibodies blocked rosette formation. Endogenous labeling experiments demonstrated that the patient's cells produced IgG both of the membrane and of the secretory type. The latter molecular form was also actively secreted. Ultrastructural studies demonstrated that the malignant clone comprised cells at different maturational stages and with different secretory properties. These findings were confirmed by the analysis of intracytoplasmic acid hydrolases, which are normally expressed at late maturational stages. These data are consistent with the hypothesis that a process of maturation was occurring within the malignant clone.

Membrane-bound and secreted IgA contain structurally different alpha-chains

Three different forms of alpha-chains are synthesized by BF0.3 and 615.2, two cloned cell lines derived from the murine B lymphoma 1.29. The three forms of alpha-chains differ in size, pI, cellular location, and rate of turnover. They were identified by means of lactoperoxidase-catalyzed radioiodination, internal 14C or 35S labeling, and immunofluorescence techniques as membrane-bound(alpha m), secreted (alpha s), and intracellular (alpha ic) proteins. Comparison of immunoglobulin products of the two lymphoma lines with those of a hybridoma cell line, Id 150, which secretes IgA of the 1.29 idiotype but lacks membrane IgA, confirmed the assignments of alpha m, alpha s, and alpha ic. Results of biosynthetic labeling of BF0.3, 615.2, and Id 150 in the presence and absence of tunicamycin suggest that the difference in m.w. and charge observed between alpha m and alpha s can be attributed to differences in primary amino acid structure rather than different degrees of glycosylation.

Membrane-bound and secreted IgA contain structurally different alpha-chains

Three different forms of alpha-chains are synthesized by BF0.3 and 615.2, two cloned cell lines derived from the murine B lymphoma 1.29. The three forms of alpha-chains differ in size, pI, cellular location, and rate of turnover. They were identified by means of lactoperoxidase-catalyzed radioiodination, internal 14C or 35S labeling, and immunofluorescence techniques as membrane-bound(alpha m), secreted (alpha s), and intracellular (alpha ic) proteins. Comparison of immunoglobulin products of the two lymphoma lines with those of a hybridoma cell line, Id 150, which secretes IgA of the 1.29 idiotype but lacks membrane IgA, confirmed the assignments of alpha m, alpha s, and alpha ic. Results of biosynthetic labeling of BF0.3, 615.2, and Id 150 in the presence and absence of tunicamycin suggest that the difference in m.w. and charge observed between alpha m and alpha s can be attributed to differences in primary amino acid structure rather than different degrees of glycosylation.

Synthesis and processing of the alpha heavy chains of secreted and membrane-bound IgA

We have compared the synthesis and processing of immunoglobulin alpha chains in two murine cell lines, a B cell lymphoma that expresses membrane-bound IgA and a hybridoma that secretes IgA. Results of biosynthetic labeling experiments demonstrated that membrane-bound and secreted alpha chains have two distinct intracellular precursors, of different molecular weights and isoelectric points. RNAs from both of these cell lines direct the synthesis in vitro of two alpha polypeptides of Mr 59,000 and 62,000, the larger one being the precursor for membrane-bound alpha chain and the smaller one being the precursor for secreted alpha chain. These cell lines each contain three RNAs, 1.7, 2.1, and 3.1 kilobases in length, which hybridize with cDNA for the alpha constant region and which are present in different concentrations. Our results suggest that the smallest RNA encodes the secreted alpha chain and one or both of the larger RNAs encode(s) the membrane-bound alpha chain.

A spatial association between membrane IgD and the receptor for C3b (CR1) at the cell surface of murine B lymphocytes

Surface immunoglobulin D (SIgD) and receptors for C3b (CR1) were demonstrated to be closely associated at the surface of mouse spleen lymphocytes. When SIgD was modulated by incubation at 37 degrees C with heteroantisera (rabbit) or monoclonal alloantibodies specific for delta-chains, the number of splenocytes capable of forming rosettes with EAC1-3b decreased by about 40%, whereas a smaller effect (13%) could be observed when EAC1-3d (indicators for CR2) were used. Antibodies to surface IgM were not inhibitory, ruling out the possibility of nonspecific inhibition of the C receptor sites by antigen-antibody complexes formed at the cell surface. In addition, co-capping of IgD and cR1 was observed on 65% of the cells expressing both markers. In these experiments IgM was shown to redistribute independently from both CR1 and CR2. CR2 and IgD also capped independently. Taken together with the observations that IgD and CR are ontogenetically related and that they have in common certain biologic properties (such as sensitivity to proteolytic enzymes and rate of turnover), these data suggest a functional relationship between the 2 surface receptors. A possible role in the mechanism of B lymphocyte triggering is discussed.

A spatial association between membrane IgD and the receptor for C3b (CR1) at the cell surface of murine B lymphocytes

Surface immunoglobulin D (SIgD) and receptors for C3b (CR1) were demonstrated to be closely associated at the surface of mouse spleen lymphocytes. When SIgD was modulated by incubation at 37 degrees C with heteroantisera (rabbit) or monoclonal alloantibodies specific for delta-chains, the number of splenocytes capable of forming rosettes with EAC1-3b decreased by about 40%, whereas a smaller effect (13%) could be observed when EAC1-3d (indicators for CR2) were used. Antibodies to surface IgM were not inhibitory, ruling out the possibility of nonspecific inhibition of the C receptor sites by antigen-antibody complexes formed at the cell surface. In addition, co-capping of IgD and cR1 was observed on 65% of the cells expressing both markers. In these experiments IgM was shown to redistribute independently from both CR1 and CR2. CR2 and IgD also capped independently. Taken together with the observations that IgD and CR are ontogenetically related and that they have in common certain biologic properties (such as sensitivity to proteolytic enzymes and rate of turnover), these data suggest a functional relationship between the 2 surface receptors. A possible role in the mechanism of B lymphocyte triggering is discussed.

The ontogeny of B lymphocytes. V. Lipopolysaccharide-induced changes of IgD expression on murine B lymphocytes

Murine splenocytes contain two minor subpopulations of B cells, one inducible by lipopolysaccharide to convert within 2 h from IgD- to IgD+ and the other to change from IgD+ TO IgD-. These two subpopulations can be separated by density centrifugation. Their relative proportions show a marked age dependency: IgD- leads to IgD+ cells are more frequent in suckling mice, while IgD+ leads to IgD- inducible cells become predominant in mice older than 3 weeks. The age dependency observed in the relative proportions between the two cell types suggest that they are ontogenetically related as progenitor-successor. This hypothesis is corroborated by phenotype analysis of the two subsets, revealing IgD- leads to IgD+ cells as IgM+, Ia+, complement receptor- (CR-) and IgD+ leads to IgD- cells as IgM+, Ia+, CR+. Our data show that IgD and CR are expressed concomitantly during B cell differentiation. On further differentiation, induced by lipopolysaccharide, both markers are lost from the cell surface at different rates: IgD decreases significantly in a very short period (less than 2.5 h) while induction of a decline in CR requires longer culture periods (greater than 8 h). Th: loss of IgD may thus herald an early differentiation event toward antibody-producing cells.