Overexpression of peroxiredoxins I, II, III, V, and VI in malignant mesothelioma

Peroxiredoxins (Prxs) are a recently characterized group of thiol-containing proteins with efficient antioxidant capacity, capable of consuming hydrogen peroxide in living cells. Altogether six distinct Prxs have been characterized in mammalian tissues. Their expression was investigated in histological samples of mesothelioma and in cell lines established from the tumours of mesothelioma patients. Four cases with histopathologically healthy pleura from non-smokers were used as controls. Healthy pleural mesothelium was negative or very weakly positive for all Prxs. In mesothelioma, the most prominent reactivity was observed with Prxs I, II, V, and VI. Prx I was highly or moderately expressed in 25/36 cases, the corresponding figures for Prxs II-VI being 27/36 (Prx II), 13/36 (Prx III), 2/36 (Prx IV), 24/36 (Prx V), and 30/36 (Prx VI). Positive staining was observed both in the cytosolic and the nuclear compartment, with the exception of Prx III, which showed no nuclear reactivity. The staining pattern of Prxs III and V was granular. Immunoelectron microscopic localization of Prxs was in accordance with the immunohistochemical findings, showing diffuse cytoplasmic localization for Prxs I, II, IV, and VI and distinct mitochondrial labelling for Prxs III and V. There was no significant association between the extent of staining and different Prxs. It appeared that Prxs may not have prognostic significance, but being prominently expressed in most mesotheliomas these proteins, at least in theory, may play a role in the primary drug resistance of this disease.     

Characterization of neural cell types expressing peroxiredoxins in mouse brain

The differential expression patterns of antioxidant enzymes observed in the brains of patients with neurodegenerative diseases suggest an important role for reactive oxygen species and antioxidant enzymes in neurodegeneration. The six mammalian peroxiredoxins (Prxs) comprise a novel family of anti-oxidative proteins that are widely distributed in most tissues, but few studies of Prx in brain tissue have been reported. The specific histology of the neural cell types in which Prxs are expressed is an important issue related to biological function and defense against oxidative stress in the brain. This study analyzed mouse brain neural cell types expressing Prx isoforms using single- or double-label immunohistochemical techniques. In neurons, immunoreactivity for Prx II-V was observed in the cytoplasm. In particular, Prx II was found in the habenular nuclei, and Prx III and V were found in the stratum lucidum of the hippocampus. Astrocytes and microglia were immunoreactive only for Prx VI and Prx I, respectively. Prx I and IV immunoreactivity was apparent in oligodendrocytes, where it was principally localized in the nuclei. The observed distribution of Prx isoforms in the mammalian brain may be indicative of their specific roles in their preferred neural cell types and subcellular locales. The results of this study will help in unraveling the physiological and pathophysiological roles of the different Prx isoforms in neural function.     

A mouse myeloma variant with a defect in light chain synthesis.

A spontaneous assembly variant, B 50, has been isolated from the MPC-11 mouse myeloma cell line. This variant synthesizes fewer light chains per cell than the parent resulting the production of a slight molar excess of heavy chains. These changes are associated with a delay and change in the pathway of assembly and a delay in secretion. Spontaneous revertants of B 50 have been obtained, all of which synthesize normal amounts of light chains and assemble and secrete the immunoglobulin molecule through the same pathways and with the same kinetics as the parental cells. A comparison of the tryptic-chymotryptic peptides of the parental, variant and revertant heavy and light chains did not reveal any differences. These studies indicate that variants in mouse myeloma cells can arise with defects in the quantitative expression of the immunoglobulin gene and suggest that the presence of excess light chains facilitates the assembly and secretion of some immunoglobulin molecules.     

Overoxidation of peroxiredoxins in vivo in cultured human umbilical vein endothelial cells and in damaging light-exposed mouse retinal tissues

Reduced and overoxidized forms of peroxiredoxins (Prxs) in vivo were assessed in cultured human umbilical vein endothelial cells (HUVEC) and in damaging light-exposed mouse retinal tissues by two-dimensional (2D) gel electrophoresis and Western blot analysis. Acidic isoelectric point (pI) shift of protein spots of Prx2, 3, 4, and 6, which indicate formation of overoxidized Prx was clearly observed after treatment with H₂O₂ but was not observed after treatment with the radical initiators 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) and 2,2′-azobis [2-(2-imidazolin-2-yl)propane] dihydrochloride (AIPH); this finding indicated selective oxidation of Prx molecules by H₂O₂. Following the exposure of the eyes of mice to visible light (5000 lx) for up to 4 h, no acidic spot shift was observed in Prx1, 2, and 6 in both retinal and retinal pigment epithelial samples; this finding indicated the possible involvement of the photosensitization reaction rather than free radicals derived from H₂O₂ in this pathology. Detection of overoxidized Prxs may be applicable for assessing the mechanisms of cell/tissue damage caused by oxidative stress in vivo.     

Structure-based insights into the catalytic power and conformational dexterity of peroxiredoxins

Peroxiredoxins (Prxs), some of nature's dominant peroxidases, use a conserved Cys residue to reduce peroxides. They are highly expressed in organisms from all kingdoms, and in eukaryotes they participate in hydrogen peroxide signaling. Seventy-two Prx structures have been determined that cover much of the diversity of the family. We review here the current knowledge and show that Prxs can be effectively classified by a structural/evolutionary organization into six subfamilies followed by specification of a 1-Cys or 2-Cys mechanism, and for 2-Cys Prxs, the structural location of the resolving Cys. We visualize the varied catalytic structural transitions and highlight how they differ depending on the location of the resolving Cys. We also review new insights into the question of how Prxs are such effective catalysts: the enzyme activates not only the conserved Cys thiolate but also the peroxide substrate. Moreover, the hydrogen-bonding network created by the four residues conserved in all Prx active sites stabilizes the transition state of the peroxidatic S(N)2 displacement reaction. Strict conservation of the peroxidatic active site along with the variation in structural transitions provides a fascinating picture of how the diverse Prxs function to break down peroxide substrates rapidly.     

Oxidative/nitrosative stress and peroxiredoxin 2 are associated with grade and prognosis of human renal carcinoma

Peroxiredoxins (Prxs) 1-6 were assessed in 138 renal cell carcinomas (RCC) using immunohistochemistry and selected samples by Western blotting analysis. Oxidative/nitrosative damage was evaluated using nitrotyrosine immunoreactivity. The expressions of Prxs were correlated with tumor grade and survival and nitrotyrosine reactivity. Non-malignant kidney tubular cells showed positivity with variable intensity for all six Prxs. In RCCs, most cases were positive for Prxs 1 and 2, while only 15-20% of tumors showed expression for Prxs 3 and 4. Prx 2 was associated with tumors of a lower grade (p=0.009) and with a lower frequency of distant metastases (p=0.046). Patients with tumors expressing Prx2 had better prognosis (p=0.027). Instead, nitrotyrosine was significantly associated with high grade tumors (p=0.001). Compared with the non-malignant kidney tubular cells, low Prx expression in the tumor cells can make them more susceptible to oxidative damage. Prx 2 was more abundantly expressed in low grade tumors, suggesting that this protein could play a role in preventing the development of oxidative damage, which in turn can lead to the activation of pathways leading to aggressive tumors.     

Expression of surface and secreted IgG22a by a murine B-lymphoma before and after hybridization to myeloma cells

A20 is a spontaneous Balb/c murine lymphoma which has been reported to express immunoglobulin, Fc receptors, and la antigens, but not complement receptors, on its cell surface. Approximately 0.1% of the protein synthesized by a subclone of A20 (A20-1.11) is IgG_2a,which is present on the cell surface as well as secreted by the cells. Biosynthetic labeling studies reveal that A20-1.11 cells synthesize a single κ light chain as well as two species of intracellular γ_2a heavy chain. The smaller γ_2a heavy chain, with a molecular weight of 62,000 daltons, is the intracellular precursor to a 64,000 dalton γ_2a heavy chain which is present in secreted IgG_2a. The larger intracellular γ_2a heavy chain, with a molecular weight of 68,000 daltons, is the intracellular precursor to a 70,000 dalton γ_2a heavy chain which is present in surface IgG_2a. Fusion of A20-1.11 lymphoma cells to murine myeloma cells results in hybrids expressing the more differentiated myeloma phenotype. That is, the expression of the secreted form of the lymphoma IgG_2a is amplified as much as 150 fold while the expression of the surface form of the lymphoma IgG_2a is abolished in the hybrid. The relationship of the γ_2a heavy chains expressed in these cells is discussed in relation to what has been reported for surface and secreted μ heavy chains.     

Fusion between immunoglobulin-secreting and nonsecreting myeloma cell lines

The defects in two nonsecreting variant clones of the mouse plasmacytoma MOPC 21 (P3) were studied by tissue culture methods. The variants (NSI and NSIII) do not synthesize detectable heavy chains. NSI synthesizes, but does not secrete, light chains and NSIII does not synthesize light chain. A screening procedure was used allowing the detection of revertant cells secreting immunoglobulin. The method is based on a hemolytic plaque assay using anti-immunoglobulin-coated red cells. No revertants were detected among 2 × 10⁷ cells. Both variant lines were fused to another myeloma line (PI) which secretes a complete immunoglobulin and excess light chains. Analysis of the products by isoelectric focusing showed that in the hybrids there was no reactivation of synthesis of the nonexpressed chains. The defects leading to loss of synthesis cannot therefore be complemented in the hybrid lines. The secretion of light chain in NSI, on the other hand, could be complemented in the hybrid but the light chain was only secreted as part of a new immunoglobulin hybrid molecule.     

Induction of peroxiredoxins in transplanted livers and demonstration of their in vitro cytoprotection activity

Peroxiredoxin (Prx)-I and -II belong to a new class of antioxidants. Here, we report that they are induced by ischemia/reperfusion (I/R) in transplanted livers. Hypothesizing that Prxs are induced to protect liver from oxidative damage, we transduced these human genes into murine NIH-3T3 cells. The overexpressed Prxs made the cells more resistant to t-butylhydroperoxide-induced apoptosis. These results indicate that Prx-I and Prx-II are induced by the transplantation process and can protect cells against oxidant damage in tissue culture. Thus, proper genetic manipulations of Prxs may be useful in increasing the success rate of organ transplantation.     

Controlled elimination of intracellular H(2)O(2): regulation of peroxiredoxin, catalase, and glutathione peroxidase via post-translational modification

The predominant enzymes responsible for elimination of hydrogen peroxide (H(2)O(2)) in cells are peroxiredoxins (Prxs), catalase, and glutathione peroxidases (GPxs). Evidence suggests that catalytic activities of certain isoforms of these H(2)O(2)-eliminating enzymes are extensively regulated via posttranslational modification. Prx I and Prx II become inactivated when phosphorylated on Thr(90) by cyclin B-dependent kinase Cdc2. In addition, the active-site cysteine of Prx I-IV undergoes a reversible sulfinylation (oxidation to cysteine sulfinic acid) in cells. Desulfinylation (reduction to cysteine) is achieved by a novel enzyme named sulfiredoxin. c-Abl and Arg nonreceptor protein tyrosine kinases associate with catalase in cells treated with H(2)O(2) by mechanisms involving the SH3 domains of the kinases and the Pro(293)PheAsnPro motif of catalase and activate catalase by phosphorylating it on Tyr(231) and Tyr(386). Similarily, GPx1 is activated by c-Abl- and Arg-mediated phosphorylation. The tyrosine phosphorylation is critical for ubiquitination-dependent degradation of catalase.     

Gene characteristics,immune and stress responses of PmPrx1 in black tiger shrimp (Penaeus monodon): Insights from exposure to pathogenic bacteria and toxic environmental stressors

Peroxiredoxins (Prxs) are ubiquitous, multifunctional and evolutionarily conserved enzymes that can protect cells from oxidative damage caused by ROS and play a vital role in immune responses. Here, a full-length Prx1 cDNA sequence (PmPrx1) was isolated from Penaeus monodon. The PmPrx1 cDNA was 951 base pairs (bp), encoding 198 amino acid polypeptides. The results of qRT-PCR showed that the PmPrx1 mRNA was ubiquitously expressed in all tissues tested and had a comparatively high expression level in immune-associated tissues (gill, hepatopancreas). To explore the immune and anti-stress roles of PmPrx1, the gills and hepatopancreas were chosen as target tissues in Penaeus monodon and were challenged with bacteria (Vibrio harveyi and Streptococcus agalactiae) and toxic environmental stresses. To further clarify the immune function of PmPrx1 after bacterial challenge, the recombinant PmPrx1 protein was acquired using a prokaryotic expression method. The antioxidant activity of the recombinant PmPrx1 was assessed by the catalyzing hydrogen peroxide assay method, and the results showed obvious antioxidant activity in a dose-dependent and temperature-dependent manner. The antimicrobial activity of purified PmPrx1 protein was evaluated and further studied in vitro relying on a bacterial growth inhibition test which was conducted in both liquid and solid cultures. Furthermore, E. coli transferred with pRSET-PmPrx1 was dramatically protected in response to metal toxicity and H₂O₂ oxidative stress. In summary, this study provides useful information about the role of the Prx1 gene in defense against a variety of toxic factors in shrimps that help to further clarify the functional mechanism of Prx.     

The synthesis and assembly of immunoglobulins by malignant human plasmacytes. III. Heterogeneity in IgA polymer assembly

The pathways of immunoglobulin synthesis and assembly have been studied in bone marrow cells obtained from 9 patients whose serum contained substantial amounts of homogeneous IgA1 myeloma proteins. Eight of the 9 cell samples synthesized light chains in excess of heavy chains. A variety of assembly intermediates, including αL, α₂ and α₂L, were also noted. The major intracellular molecule in most cases was α₂L₂ although larger polymers were noted in the secretions and serum of most of the patients. In only one instance was a large amount of polymer larger than α₂L₂ found inside the cell. As is the case for the assembly for IgM, the sites of IgA polymer assembly and factors responsible for the observed heterogeneity have not yet been established.     

From cytoprotection to tumor suppression: the multifactorial role of peroxiredoxins

In the past decade, a new family of highly conserved antioxidant enzymes, Peroxiredoxins (Prxs), have been discovered and defined. There are two major Prx subfamilies: one subfamily uses two conserved cysteines (2-Cys) and the other uses 1-Cys to scavenge reactive oxygen species (ROS). This review focuses on the four mammalian 2-Cys members (Prx I-IV) that utilize thioredoxin as the electron donor for antioxidation. The array of biological activities of these proteins suggests that they may be evolutionarily important for cell function. For example, Prxs are capable of protecting cells from ROS insult and regulating the signal transduction pathways that utilize c-Abl, caspases, nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) to influence cell growth and apoptosis. Prxs are also essential for red blood cell (RBC) differentiation and are capable of inhibiting human immunodeficiency virus (HIV) infection and organ transplant rejection. Distribution patterns indicate that Prxs are highly expressed in the tissues and cells at risk for diseases related to ROS toxicity, such as Alzheimer's and Parkinson's diseases and atherosclerosis. This interesting correlation suggests that Prxs are protective against ROS toxicity, yet overwhelmed by oxidative stress in some cells. Prxs tend to form large aggregates at high concentrations, a feature that may interfere with their normal protective function or may even render them cytotoxic. Imbalance in the expression of subtypes can also potentially increase their susceptibility to oxidative stress. Understanding the function and biological role of Prxs may lead to important discoveries about the cellular dysfunction of ROS-related diseases ranging from atherosclerosis to cancer to neurodegenerative diseases.     

A Mott cell hybridoma

A hybridoma is described that exhibits all the characteristic features of Mott cells. It has spherules (Russell bodies) in the cytoplasm made up of dilated rough endoplasmatic reticulum and containing condensed immunoglobulin (λ₁ light chains). Some of the cells appear to be very fragile, and free spherules are often found on cell smears. Cells with the Mott cell characteristics are still able to divide, but they do not secrete immunoglobulin. Hybridomas of this kind should be useful for determining the place of the Mott cell within the scheme of B cell differentiation.     

Fidelity and infidelity in commitment to B‐lymphocyte lineage development

Summary: During B‐lymphocyte development in mouse fetal liver and bone marrow, a pre‐B I cell stage is reached in which the cells express B‐lineage‐specific genes, such as CD19, Iga and Igb, and V_preB and l5, which encode the surrogate light (SL) chain. In these pre‐B I cells both alleles of the immunoglobulin heavy (IgH) chain locus are D_H J_H rearranged. Transplantation of pre‐B I cells from wild‐type (e.g. C57Bl/6) mice in histocompatible RAG‐deficient hosts leads to long‐term reconstitution of some of the mature B‐cell compartments and to the establishment of normal IgM levels, a third of the normal serum IgA levels, and IgG levels below the detection limit. Neither T‐lineage nor myeloid cells of donor origin can be detected in the transplanted hosts, indicating that the pre‐B I cells are committed to B‐lineage differentiation. Consequently, the B‐cell‐reconstituted hosts respond to T‐cell‐independent antigens but not to T‐cell‐dependent antigens. Responses to T‐cell‐dependent antigens can be restored in the pre‐B I‐cell‐transplanted, RAG‐deficient hosts by the concomitant transplantation of mature CD4+ T cells. The transplanted wild‐type pre‐B I cells do not home back to the bone marrow and become undetectable shortly after transplantation. B‐lymphocyte development in Pax‐5‐deficient mice becomes arrested at the transition of pre‐B I to pre‐B II cells i.e. at the stage when V_H to D_HJ_H rearrangements occur and when the pre‐B‐cell receptor, complete with H chains and SL chains, is normally formed. T‐lineage and myeloid cell development in these mice is normal. Pre‐B I cells of Pax‐5‐deficient mice have a wild‐type pre‐B I‐cell‐like phenotype: while they do not express Pax‐5‐controlled CD19 gene, and express Iga to a lesser extent, they express Igb, V_preB and l5, and proliferate normally in vitro on stromal cells in the presence of interleukin (IL)‐7. Clones of these pre‐B I cells carry characteristic D_H J_H rearrangements on both IgH chain alleles. However, removal of IL‐7 from the tissue cultures, unlike wild‐type pre‐B I cells, does not induce B‐cell differentiation to surface IgM‐expressing B cells, but induces macrophage differentiation. This differentiation into macrophages requires either the presence of stromal cells or addition of macrophage colony‐stimulating factor (M‐CSF). Addition of M‐CSF followed by granulocyte–macrophage colony‐stimulating factor induces the differentiation to MHC class II‐expressing, antigen‐presenting dendritic cells. In vitro differentiation to granulocytes and osteoclasts can also be observed in the presence of the appropriate cyto­kines. Moreover, transplantation of Pax‐5‐deficient pre‐B I clones into RAG‐deficient hosts, while not allowing B‐cell differentiation, leads to the full reconstitution of the thymus with all stages of CD4–CD8– and CD4+CD8+ thymocytes, to normal positive and negative selection of thymocytes in the thymus, and to the development of normal, reactive mature CD4+ and CD8+ T‐cell compartments in the peripheral lymphoid tissues, all carrying the clone‐specific D_H J_H rearrangements. On the other hand, Iga, Igb, V_preB and l5 are turned off in the thymocytes, demonstrating that the expression of these genes does not commit cells irreversibly to the B lineage. Furthermore, Pax‐5‐deficient pre‐B I cells are long‐term reconstituting cells. They home back to the bone marrow of the RAG‐deficient host, can be reisolated and regrown in tissue culture, and can be retransplanted into a secondary RAG‐deficient host. This again develops thymocytes and mature T cells and allows the transplanted clonal pre‐B I cells to home to the bone marrow.     

Multiple functions of peroxiredoxins: peroxidases, sensors and regulators of the intracellular messenger H₂O₂, and protein chaperones

Peroxiredoxins (Prxs) are a family of peroxidases that reduce peroxides, with a conserved cysteine residue (the peroxidatic Cys) serving as the site of oxidation by peroxides. Peroxides oxidize the peroxidatic Cys-SH to Cys-SOH, which then reacts with another cysteine residue (typically the resolving Cys [C(R)]) to form a disulfide that is subsequently reduced by an appropriate electron donor. On the basis of the location or absence of the C(R), Prxs are classified into 2-Cys, atypical 2-Cys, and 1-Cys Prx subfamilies. In addition to their peroxidase activity, members of the 2-Cys Prx subfamily appear to serve as peroxide sensors for other proteins and as molecular chaperones. During catalysis, the peroxidatic Cys-SOH of 2-Cys Prxs is occasionally further oxidized to Cys-SO(2)H before disulfide formation, resulting in inactivation of peroxidase activity. This hyperoxidation, which is reversed by the ATP-dependent enzyme sulfiredoxin, modulates the sensor and chaperone functions of 2-Cys Prxs. The peroxidase activity of 2-Cys Prxs is extensively regulated via tyrosine and threonine phosphorylation, which allows modulation of the local concentration of the intracellular messenger H(2)O(2). Finally, 2-Cys Prxs interact with a variety of proteins, with such interaction having been shown to modulate the function of the binding partners in a reciprocal manner.     

IMMUNOGLOBULIN EVOLUTION: CHEMICAL STUDY OF CLAWED TOAD (XENOPUS LAEVIS) HEAVY AND LIGHT CHAINS

NH₂, terminal amino acid sequence determinations of clawed toad (Xenopus laevis) immunoglobulins indicate that approximately 30% of the heavy chains and less than 5% of the light chains have unblocked NH₂ termini. The major amino acid sequence of the X. laevis 7S immunoglobulin heavy chains is the same as that of the 19S immunoglobulin heavy chains. Thus in the synthesis of the heavy chains, the V_H genes coding for unblocked heavy chains can associate with C_H genes of both the 19S and 7S classes. This association is particularly important in amphibians because, in contrast to mammals and birds, the majority of amphibian antibody-producing cells synthesize both 19S and 7S immunoglobulins and do not participate in the ‘genetic switch’ characteristic of lymphocyte differentiation in higher organisms. In X. laevis, the major amino acid sequence at the first twenty-four positions of the unblocked heavy chains shows approximately 54% difference from the prototype amino acid sequence of the mammalian V_HIII subgroup. Thus, the V_HIII gene(s) must have started to appear after the evolutionary divergence of the common ancestor of mammals and birds from the amphibian line. The amino acid composition of the X. laevis 7S immunoglobulin heavy chains differs from that of its 19S immunoglobulins as well as those of human IgG and IgA. These data support the concepts (a) that amphibian 7S and 19S immunoglobins belong to distinct classes and (b) that amphibian 7S immunoglobulin does not resemble mammalian IgG or IgA.     

Derivation of specific antibody-producing tissue culture and tumor lines by cell fusion

Cell fusion techniques have been used to produce hybrids between myeloma cells and antibody-producing cells. The hybrid lines derived are permanently adapted to grow in tissue culture and are capable of inducing antibody-producing tumors in mice. Spleens from mice immunized against sheep red blood cells (SRBC) were fused to an 8-azaguanine-resistant clone (X63-Ag8) of MOPC 21 myeloma. Over 50 % of the derived hybrid lines produce and secrete immunoglobulins different from the MOPC 21 myeloma. About 10 % of the hybrid lines exhibit anti-SRBC activity. The high proportion of antibody-producing hybrids suggests that the fusion involves a restricted fraction of the spleen cell population, probably cells committed to antibody production. In order to avoid the presence of the MOPC 21 heavy chain in the specific hybrids, another myeloma cell line (NSI/1-Ag4–1) has been used. This is a nonsecreting variant of the MOPC 21 myeloma which does not express heavy chains. Three anti-SRBC (probably of the μ, γ_2b and γ₁ classes, respectively) and two anti-2,4,6-trinitrophenyl (of the μ class) antibody-producing hybrids have been repeatedly cloned. By random selection and by selection of specific clones according to their lytic activity (clone plaque selection), a number of different lines have been constructed. Such lines express different combinations of the four possible chains of each hybrid line: the myeloma γ and k chains and the specific antibody heavy and light chains. In three cases (Sp1, Sp2 and Sp7) it is shown that only the specific H and L combination has activity and that the myeloma chains are unable to substitute for them. In most cases lines have been derived which no longer express the MOPC 21 chains but only the specific antibody chains.     

Intracytoplasmic and surface-bound immunoglobulins in "nonsecretory" and Bence-Jones myeloma.

Immunoglobulins were studied at the cellular level by direct immunofluorescence in twenty-five patients with ''nonsecretory'' myeloma and thirty-six patiens with Bence-Jones (BJ) myeloma. The results were compared with those obtained in a control group of thirty-six patients with common secretory myeloma. A monoclonal Ig (IgG in eighteen, IgA in three and kappa chains only in three cases) was found in the cytoplasm of the plasma cells from all the patients with ''nonsecretory'' myeloma, with a striking dysbalance in the staining brightness for the heavy and the light chains. A similar dysbalance in staining was also observed for plasma cell surface Ig chains but in the opposite way. In twenty patients with BJ myeloma studied for cytoplasmic Ig only, determinants of a heavy chain were clearly found in four cases. When surface Ig were studied also, the production of gamma chains in addition to the light chain could be ascertained in six of sixteen cases. In addition, IgM with the same light chain type as the BJ protein was detected at the cell surface on plasma cells and lymphocytes in two of these sixteen patients. ''Monoclonal'' populations of B lymphocytes bearing the same Ig chains as those produced by the myeloma cells were detectable in five of eleven ''nonsecretory'' myeloma and in five of sixteen BJ myeloma patients. Normal blood B lymphocytes were in decreased number, particularly when a ''monoclonal'' lymphocytic population was detected. Data are discussed which suggest that plasma cells from most patients with ''nonsecretory'' myeloma might synthesize and secrete Ig molecules with structurally abnormal chains that are then quickly degraded.