Autoimmune Hypercalcemia Due to Autoantibodies Against the Calcium-sensing Receptor

CONTEXT

Autoimmune hypocalciuric hypercalcemia (AHH) is an acquired disorder caused by the presence of blocking autoantibodies against the calcium-sensing receptor (CaSR). Few cases of this condition have been described to date in the literature.

OBJECTIVE

The objectives of this study were to describe 2 patients in whom the presence of AHH was suspected and to assess the patients for the presence of CaSR antibodies.

METHODS

CaSR antibodies were detected and characterised by immunoprecipitation assays, CaSR peptide ELISAs, and functional assays based on the calcium-stimulated accumulation of inositol-1-phosphate in a mammalian cell line expressing the CaSR.

RESULTS

Both patients presented with an acquired form of hypocalciuric hypercalcemia. Mutational analyses of CASR, GNA11, and AP2S1 for familial hypocalciuric hypercalcemia were negative. According to the presence of Hashimoto's disease in 1 patient and latent autoimmune diabetes of adulthood and thyroid autoimmunity in the other, AHH was suspected. Immunoprecipitation assays detected CaSR antibodies in both patients. Analysis of the antibody binding sites revealed 2 main epitopes at amino acids 41-69 and 114-126. Preincubation with purified CaSR antibodies against epitope 114-126 resulted in a significant decrease in inositol-1-phophate accumulation upon calcium-stimulation of mammalian cells expressing the CaSR, suggesting that the antibodies had receptor-blocking activity.

CONCLUSIONS

AHH is to be suspected in patients with an acquired biochemical pattern of PTH-dependant hypocalciuric hypercalcemia, especially in those with other concomitant autoimmune diseases. Diagnosis by means of detecting CaSR antibodies may help to better characterise this probably under-reported condition.

Immune-Active Microenvironment in Small Cell Carcinoma of the Ovary, Hypercalcemic Type: Rationale for Immune Checkpoint Blockade

Small cell carcinoma of the ovary, hypercalcemic type (SCCOHT), is a highly aggressive monogenic cancer driven by SMARCA4 mutations. Here, we report responses to anti-PD1 immunotherapy in four patients and characterize the immune landscape of SCCOHT tumors using quantitative immunofluorescence and gene expression profiling. Unexpectedly for a low mutation burden cancer, the majority of the tumors (eight of 11 cases) demonstrated PD-L1 expression with strong associated T-cell infiltration (R2 = 0.60-0.95). PD-L1 expression was detected in both tumor and stromal cells, with macrophages being the most abundant PD-L1-positive cells in some tumors (three of 11 cases). Transcriptional profiling revealed increased expression of genes related to Th1 and cytotoxic cell function in PD-L1-high tumors, suggesting that PD-L1 acts as a pathway of adaptive immune resistance in SCCOHT. These findings suggest that although SCCOHT are low-mutational burden tumors, their immunogenic microenvironment resembles the landscape of tumors that respond well to treatment with PD-1/PD-L1 blockade.

Glucocorticoid-responsive lymphocytic parathyroiditis and hypocalciuric hypercalcemia due to autoantibodies against the calcium-sensing receptor: a case report and literature review

OBJECTIVE

Autoimmune lymphocytic parathyroiditis and acquired hypocalciuric hypercalcemia associated with autoantibodies against the calcium-sensing receptor (anti-CaSR) are rare and poorly understood conditions. Here, we describe a patient with acquired parathyroid hormone (PTH)-dependent hypercalcemia with associated hypocalciuria, found to have true lymphocytic parathyroiditis on histopathology, and circulating anti-CaSR antibodies in serum.

DESIGN AND METHODS

A 64-year-old woman was referred to our clinic for persistent hypercalcemia after a subtotal parathyroidectomy. She was normocalcemic until the age of 63 years when she was diagnosed with primary hyperparathyroidism. She underwent subtotal parathyroidectomy with appropriate intraoperative PTH decline. Two weeks post-parathyroidectomy, she presented with persistent hypercalcemia and hyperparathyroidism. Urine studies revealed an inappropriately low 24-h urine calcium (Ca)/creatinine clearance ratio. Surgical pathology was consistent with true lymphocytic parathyroiditis with lymphoid follicles. The presence of circulating anti-CaSR antibodies was detected by immunoprecipitation of CaSR by the patient's serum. After a 4-week course of prednisone, serum Ca and PTH normalized, and her anti-CaSR titers declined. She remains normocalcemic 10 months after the discontinuation of glucocorticoid therapy. We present this patient in the context of the relevant published literature on lymphocytic parathyroiditis and acquired hypocalciuric hypercalcemia related to anti-CaSR antibodies.

CONCLUSIONS

Autoimmune lymphocytic parathyroiditis and acquired hypocalciuric hypercalcemia associated with anti-CaSR antibodies is a very rare yet important condition to be considered in a patient with acquired PTH-dependent hypercalcemia with inappropriate hypocalciuria. Although subtotal parathyroidectomy is unlikely to correct the hypercalcemia, this entity may respond to a short course of prednisone therapy.

Biased agonism: a novel paradigm in G protein-coupled receptor signaling observed in acquired hypocalciuric hypercalcemia

The classical model of G protein-coupled receptor (GPCR) activation is the two-state model, in which the GPCR exists in equilibrium between an active and inactive state. Based on this model, GPCR ligands have been classified as agonists, inverse agonists, or antagonists depending on their actions in shifting this equilibrium. Recently, however, accumulating evidence has indicated that GPCRs may exist in multiple active and inactive conformational states. In this situation, each ligand recognizes and stabilizes a specific conformation of the GPCR, leading to a set of specific biological effects. Based on this new model, a unique agonist or a combination of the usual agonist and an allosteric modulator may enable activation of a specific signaling pathway via a GPCR that activates multiple signals (biased agonism, functional selectivity). The calcium-sensing receptor autoantibody that we have identified in the serum of a patient with acquired hypocalciuric hypercalcemia (AHH) is the first example of a biased allosteric modulator of a GPCR working in a pathophysiological context. Our findings may indicate the presence of physiological allosteric modulators and provide new directions for the future drug development.

Autoimmune hypocalciuric hypercalcemia unresponsive to glucocorticoid therapy in a patient with blocking autoantibodies against the calcium-sensing receptor

CONTEXT

Autoantibodies directed against the calcium-sensing receptor (CaSR) have been reported in several individuals with various autoimmune disorders and PTH-mediated hypercalcemia. Previously, glucocorticoid treatment has been shown to decrease the CaSR autoantibody titers and normalize the hypercalcemia in a patient with autoimmune hypocalciuric hypercalcemia (AHH).

OBJECTIVE

The objective of the study was to evaluate a patient with AHH for the presence of blocking autoantibodies against the CaSR and to monitor her biochemical and serological responses to a trial of glucocorticoid therapy.

RESULTS

Glucocorticoid treatment had no effect on serum total or ionized calcium concentration or serum PTH levels, all of which remained at higher than normal levels. In contrast, on prednisone, urinary calcium excretion increased from overtly hypocalciuric levels to normal values. Anti-CaSR autoantibodies were detected at similar levels in the patient's serum before, during, and after glucocorticoid treatment. Functional testing of these antibodies showed that they inhibited the stimulatory effect of extracellular Ca(2+) on ERK1/2 but did not suppress the calcium-induced accumulation of inositol-1-phosphate.

CONCLUSIONS

We report a patient with AHH with frankly elevated PTH levels who was found to have autoantibodies against the CaSR. The hypercalcemia and CaSR autoantibody titers failed to respond to glucocorticoid therapy, unlike a previously reported patient with similar clinical and biochemical features. The anti-CaSR antibody-mediated inhibition of CaSR-stimulated ERK1/2 activity, but not of inositol-1-phosphate accumulation, suggests that ERK1/2 may mediate, at least in part, the regulation of PTH secretion and urinary calcium excretion by the CaSR.

Clinical significance of antibodies against calcitonin

Calcitonin (CT) inhibits osteoclast-mediated bone resorption and is being used to treat Paget's disease of bone, hypercalcemia of malignancy and postmenopausal osteoporosis. The formation of antibodies against heterologuous calcitonins like salmon calcitonin (sCT) is common and occurs in 40-70% of the patients treated for more than 4 months. Not all of these patients, however, develop a secondary resistance to sCT, therefore the clinical significance of sCT antibodies is discussed controversially. In vivo and in vitro approaches demonstrate a neutralizing effect in 35 to 60% of the patient sera with antibodies against sCT. These neutralizing antibodies appear to explain most cases of clinically relevant secondary resistance to sCT treatment, which occurs in 25-45% of the patients after treatment periods of 6 months and longer. A positive treatment response to human CT after development of secondary resistance to sCT proves the diagnosis of antibody related resistance. Few cases develop secondary resistance in the absence of sCT binding antibodies, the mechanism of this phenomenon is unclear. Antibody related resistance is a significant problem in long term treatment with sCT. Especially in conditions like postmenopausal osteoporosis, where no readily accessable marker of treatment response is available, the development of sCT antibodies and their possible neutralizing effect has to be considered.

Excessive hypercalcaemia and mixed connective tissue disease

A 23-year-old female with extreme hypercalcaemia was treated with calcitonin, mitramycin and parathyroidectomy and normocalcaemia was achieved after 4 weeks. Nevertheless, the patient later died of cutaneous necrosis, impaired circulation and multiple organ failure. Serum immunoreactive parathyroid hormone was in the normal range and parathyroid tissue normal. Mixed connective tissue disease was diagnosed on the basis of high titers of antibody to extractable nuclear antigen, moderately elevated levels of antibody to nuclear antigen and only marginal elevation of anti-double standed DNA. The role of Cl. difficile toxin in the blood and an acinic cell tumour is unclear.

Receptor activator of NF-kappa B ligand inhibition suppresses bone resorption and hypercalcemia but does not affect host immune responses to influenza infection

Receptor activator of NF-kappaB (RANK) and its ligand (RANKL) are essential for osteoclast formation, function, and survival. Osteoprotegerin (OPG) inhibits RANK signaling by sequestering RANKL. This study evaluated the antiosteoclast and immunoregulatory effects of mouse rRANK-Fc, which, similar to OPG, can bind RANKL. The effect of RANKL inhibition by RANK-Fc on osteoclast function was determined by inhibition of vitamin D(3) (1,25(OH)(2)D(3))-induced hypercalcemia. Mice were injected with a single dose of 0, 10, 100, 500, or 1000 microg of RANK-Fc; 100 microg of OPG-Fc; or 5 microg of zoledronate 2 h before 1,25(OH)(2)D(3) challenge on day 0, and sacrificed on days 1, 2, 4, 6, 8, 12, 16, and 20. RANK-Fc doses of 100 or 500 microg were tested in a mouse respiratory influenza virus host-resistance model. A single dose of RANK-Fc > or =100 microg suppressed elevation of serum calcium levels and suppressed the bone turnover marker serum pyridinoline at day 4 and later time points, similar to those observed with OPG-Fc and zoledronate (p < or = 0.01 vs controls). By day 6, both immature and mature osteoclasts were depleted by high doses of RANK-Fc (500 and 1000 microg) or 100 microg of OPG-Fc. RANK-Fc doses of 100 or 500 microg had no detectable effect on immune responses to influenza infection, as measured by activation of cytotoxic T cell activity, influenza-specific IgG response, and virus clearance. RANK-Fc inhibition of RANKL has antiosteoclast activity at doses that have no detectable immunoregulatory activity, suggesting that RANKL inhibitors be further studied for their potential to treat excess bone loss.

An acquired hypocalciuric hypercalcemia autoantibody induces allosteric transition among active human Ca-sensing receptor conformations

The seven-spanning calcium-sensing receptor (CaSR) activates multiple G proteins including Gq and Gi, and thereby activates a variety of second messengers and inhibits parathyroid hormone (PTH) secretion. However, the exact signaling mechanisms underlying the functional activity of CaSR are not yet fully understood. The heterozygous inactivation of CaSR or its inhibition by antibody blocking results in either familial hypocalciuric hypercalcemia or acquired hypocalciuric hypercalcemia (AHH), respectively. Here, we report the identification of a unique CaSR autoantibody in an AHH patient. Paradoxically, we find that this autoantibody potentiates the Ca(2+)/Gq-dependent accumulation of inositol phosphates by slightly shifting the dose dependence curve of the Ca(2+) mediated activation of phosphatidylinositol turnover to the left, whereas it inhibits the Ca(2+)/Gi-dependent phosphorylation of ERK1/2 in HEK293 cells stably expressing human CaSR. Treatment of these same cells with a calcimimetic, NPS-R-568, augments the CaSR response to Ca(2+), increasing phosphatidylinositol turnover and ERK1/2 phosphorylation, and overcoming the autoantibody effects. Our observations thus indicate that a calcium-stimulated CaSR primed by a specific autoantibody adopts a unique conformation that activates Gq but not Gi. Our findings also suggest that CaSR signaling may act via both Gq and Gi to inhibit PTH secretion. This is the first report of a disease-related autoantibody that functions as an allosteric modulator and maintains G protein-coupled receptors (GPCRs) in a unique active conformation with its agonist. We thus speculate that physiological modulators may exist that enable an agonist to specifically activate only one signaling pathway via a GPCR that activates multiple signaling pathways.

Human gamma delta T cells and tumor immunotherapy

Human Vgamma2Vdelta2 T cells recognize nonpeptide antigens derived from pathogenic microbes in a TCR-dependent manner, such as pyrophosphomonoester compounds from mycobacteria and malaria parasite and alkyl amines from Proteus, suggesting that this subset of gamma delta T cells is involved in infectious immunity. The precise recognition mechanism has been delineated using a site-directed mutagenesis strategy based on crystal structure of gamma delta TCR. On the other hand, several lines of evidence indicate that human gamma delta T cells are involved in tumor immunity. Although activated gamma delta T cells exhibit a cytolytic activity against most of tumor cells, only a small fraction of tumor cells, like Burkitt lymphoma cells and multiple myeloid cells, is recognized by human gamma delta T cells in a TCR-dependent manner. This implicates that human gamma delta T cells have two distinct pathways for anti-tumor immunity. One is a natural killer-like pathway and the other is a TCR-dependent pathway. Recently, it was shown that treatment of human tumor cells with nitrogen-containing bisphosphonates, therapeutic drugs for hypercalcemia in malignancy, generated antigenic structure on the surface of tumor cells, which could be recognized by human gamma delta T cells in a TCR-dependent manner. This tumor labeling system may lead to a novel strategy for cancer immunotherapy.

IL-4 Inhibits Bone-Resorbing Activity of Mature Osteoclasts by Affecting NF-κB and Ca2+ Signaling

IL-4 is an important immune cytokine that regulates bone homeostasis. We investigated the molecular mechanism of IL-4 action on bone-resorbing mature osteoclasts. Using a highly purified population of mature osteoclasts, we show that IL-4 dose-dependently inhibits receptor activator of NF-kappaB ligand (RANKL)-induced bone resorption by mature osteoclasts. We detected the existence of IL-4R mRNA in mature osteoclasts. IL-4 decreases TRAP expression without affecting multinuclearity of osteoclasts, and inhibits actin ring formation and migration of osteoclasts. Interestingly, IL-4 inhibition of bone resorption occurs through prevention of RANKL-induced nuclear translocation of p65 NF-kappaB subunit, and intracellular Ca(2+) changes. Moreover, IL-4 rapidly decreases RANKL-stimulated ionized Ca(2+) levels in the blood, and mature osteoclasts in IL-4 knockout mice are sensitive to RANKL action to induce bone resorption and hypercalcemia. Furthermore, IL-4 inhibits bone resorption and actin ring formation by human mature osteoclasts. Thus, we reveal that IL-4 acts directly on mature osteoclasts and inhibits bone resorption by inhibiting NF-kappaB and Ca(2+) signaling.

Macrophage inflammatory protein-1alpha induces hypercalcemia in adult T-cell leukemia

Hypercalcemia is observed in >80% of ATL. Serum MIP-1alpha levels were elevated in all 24 ATL with hypercalcemia but undetectable in all 10 patients with humoral hypercalcemia of malignancy with solid tumors and in 34 of 37 ATL without hypercalcemia. We propose that serum MIP-1alpha is a clinical hallmark for hypercalcemia in ATL.

INTRODUCTION

High serum cytokines levels are not always associated with hypercalcemia in patients with adult T-cell leukemia (ATL), suggesting that other factors are involved in the pathogenesis of ATL patients with hypercalcemia. This study was designed to determine the role of macrophage inflammatory protein-1alpha (MIP-1alpha), a chemokine recently described as an osteoclast stimulatory factor, in ATL-associated hypercalcemia.

MATERIALS AND METHODS

We measured serum interleukin (IL)-1beta, IL-6, TNF-alpha, parathyroid hormone-related protein (PTHrP), and MIP-1alpha levels in ATL patients by enzyme-linked immunosorbent assays. FACScan was used to measure the expression of RANKL on ATL cells. Osteoclast formation in cocultures of ATL cells and peripheral blood mononuclear cells (PBMCs) was evaluated by TRACP staining.

RESULTS

High serum MIP-1alpha levels were noted in all 24 ATL patients with hypercalcemia and in 3 of 37 ATL patients without hypercalcemia. The elevated levels of MIP-1alpha and calcium in ATL patients decreased after effective chemotherapy, emphasizing the role of MIP-1alpha in ATL hypercalcemia. ATL cells spontaneously produced MIP-1alpha. MIP-1alpha significantly enhanced human monocyte (precursor cells of osteoclasts) migration and induced RANKL expression on ATL cells. ATL cell-induced osteoclast formation from PBMCs was inhibited by anti-MIP-1alpha antibody and osteoprotegerin.

CONCLUSION

Our results suggest that MIP-1alpha can induce RANKL on ATL cells in autocrine fashion and that RANKL seems to mediate the hypercalcemic effect of MIP-1alpha in ATL. We propose that MIP-1alpha is the clinical hallmark of hypercalcemia in ATL and could be a potentially useful therapeutic target.

A syndrome of hypocalciuric hypercalcemia caused by autoantibodies directed at the calcium-sensing receptor

Antibodies to cell surface receptors can cause endocrine dysfunction by mimicking or blocking the actions of their respective hormones. We sought patients with autoantibodies to the extracellular calcium (Ca(2+)(o))-sensing receptor (CaR), which sets the normal level of blood calcium, that mimic the genetic disorder, familial hypocalciuric hypercalcemia, caused by heterozygous inactivating mutations of the CaR. Four individuals from two kindreds were identified with PTH-dependent hypercalcemia, who had other autoimmune manifestations: one with sprue and antigliadin and antiendomyseal antibodies and three with antithyroid antibodies. Three of the patients also had relative or absolute hypocalciuria. The patients' sera contained antibodies that reacted with the cell surface of bovine parathyroid cells in a manner similar to an authentic polyclonal anti-CaR antibody, stained bands on Western analysis of sizes similar to those labeled by the anti-CaR antiserum, and reacted with several synthetic peptides derived from sequences within the CaR's extracellular amino terminus. The patients' sera also stimulated PTH release from dispersed human parathyroid cells compared with the effect of sera from normocalcemic control subjects. This stimulation could be blocked by preabsorbing serum with membranes from CaR-transfected, but not nontransfected, human embryonic kidney (HEK293) cells. Finally, in two of the patients, antibodies affinity-purified using a synthetic peptide from within the CaR's extracellular domain inhibited high Ca(2+)(o)-stimulated, CaR-mediated accumulation of inositol phosphates and activation of mitogen-activated protein kinase in CaR-transfected HEK293 cells. DNA sequencing revealed no mutations within the index patients' CaR genes in the two families. Therefore, a biochemical phenotype of PTH-dependent hypercalcemia resembling that caused by heterozygous inactivating mutations of the CaR in familial hypocalciuric hypercalcemia can be observed in patients with antibodies to the CaR's extracellular domain that stimulate PTH release, probably by inhibiting activation of the CaR by Ca(2+)(o). Autoimmune hypocalciuric hypercalcemic is an acquired disorder of Ca(2+)(o) sensing that should be differentiated from that caused by inactivating mutations of the CaR.

Pneumocystis carinii in a patient with hypercalcemia and renal failure secondary to sarcoidosis

A case of severe dyspnea, hypercalcemia and renal failure secondary to sarcoidosis is reported. The clinical diagnosis of sarcoidosis in a 48-year-old man was confirmed by histology and cytology. Transiently decreased numbers of CD4+ T cells (282/microliter) indicated impaired immunity in the absence of HIV-infection during the acute phase of the disease. Surprisingly, numerous "trophozoites" of Pneumocystis carinii were detected by immunofluorescence staining and PCR in the bronchoalveolar fluid indicating infection or colonization of the lungs. Corticosteroid therapy was administered together with trimethoprim-sulfamethoxazole and rapidly reduced elevated serum calcium and creatinine concentrations. Since airborne person-to-person transmission of P. carinii to susceptible individuals might be possible, patients with sarcoidosis could be a previously unrecognized reservoir for P. carinii distribution in hospitals and in the community at large.

Relationship between circulating interleukin-10 (IL-10) with interleukin-6 (IL-6) type cytokines (IL-6, interleukin-11 (IL-11), oncostatin M (OSM)) and soluble interleukin-6 (IL-6) receptor (sIL-6R) in patients with multiple myeloma

We investigated the serum concentration of the interleukin-10 (IL-10), along with cytokines of interleukin-6 (IL-6) family (IL-6, IL-11 and oncostatin M - OSM), as well as soluble receptor for IL-6 (sIL-6R), in 121 patients with multiple myeloma (MM) and 28 healthy subjects. We studied the interactions between IL-10 and other cytokines, and the receptor. The correlation between IL-10 and some clinical and laboratory parameters associated with the disease activity were also analysed. The IL-10 was detectable in all patients with multiple myeloma and in all controls. The IL-10 concentration was significantly increased in myeloma patients compared with healthy persons (mean - 7.09 and 2.1 pg/ml, respectively) (p = 0.008). The level of IL-10 correlated positively with the advanced stage of disease estimated according to the Salmon and Durie classification (I versus III stage - p = 0.03). Higher values of IL-10 were found in patients with the light chain disease, hypercalcaemia, and correlated with the elevated concentrations of C-reactive protein (CRP). IL-6 was detected in 117 of the 121 patients and in all controls. The concentration of IL-6 was statistically increased in MM patients compared with control group (mean - 16.06 and 4.49 pg/ml, respectively) (p = 0.01). We found a positive correlation between IL-10 and IL-6 serum levels in MM patients. The relationship, expressed as Spearman's rank sum coefficient (rho = 0.249, p = 0.006) was significant. IL-11 was detected in 26 of the 121 MM patients and in 3 of the 28 healthy subjects at the mean concentration of 1.2 and 0.6 pg/ml respectively (p > 0.05). OSM was at detectable levels in 51 of the 121 patients and in only 4 of the 28 controls (mean - 3.84 and 0.1 pg/ml, p = 0. 002). The correlation between IL-10 and IL-11 levels in MM patients was not significant, but there was a strong statistical correlation between IL-10 and OSM concentrations (rho= 0.327, p = 0.0002). The serum concentration of sIL-6R was measurable in all patients and all controls (mean - 66.00 and 39.57 ng/ml respectively), but the difference between these groups was not significant. We found significant, positive correlation between the levels of IL-10 and sIL-6R (rho= 0.233, p = 0.01). In conclusion, we state that the serum concentrations of IL-10, IL-6, OSM and sIL-6R in MM patients may be a useful markers for the evaluation of the disease activity.

Control of hypercalcaemia of parathyroid carcinoma by immunisation

BACKGROUND

Patients with parathyroid tumours can develop extreme hypercalcaemia and osteitis fibrosa cystica. Clinical features result from the action of parathyroid hormone (PTH) on bone receptors. Because this hormone is produced in microgram quantities, inhibition of its metabolic effects with potent PTH antibodies should be possible. We tested whether an immunisation with synthetic human and bovine PTH peptides could stimulate autoantibodies against PTH.

METHODS

A patient with metastatic parathyroid carcinoma in the lungs and pleura developed severe bone disease and extreme hypercalcaemia that proved resistant to conventional therapy. She was immunised with 200 microg human and bovine PTH peptides and 50 microg human PTH. Booster doses were also given at 4 weeks and 11 weeks. The patient was then seen every week.

FINDINGS

Antibodies against PTH were produced within 4 weeks of initial immunisation and titres increased with repeated doses of immunogens. Total serum calcium concentrations, which had ranged from 3.5 mmol/L to 4.2 mmol/L over the previous 18 months, fell to between 2.5 mmol/L and 3.0 mmol/L over 6 months of therapy. This fall was accompanied by striking clinical improvement.

INTERPRETATION

We believe this is the first use of immunotherapy to control remote, non-metastatic complications of malignant disease. B-cell tolerance to human PTH was broken by immunisation with PTH peptides in adjuvant. This therapeutic approach could be used to control excess hormone production in several types of endocrine tumour and may have applications in other diseases.

A novel ALL-L3 cell line, BALM-16, lacking expression of immunoglobulin chains derived from a patient with hypercalcemia

A human acute lymphoblastic leukemia (ALL) cell line, BALM-16, was established from the peripheral blood specimen of a patient with B cell ALL L3 type (ALL-L3) in relapse. As with the original leukemia cells, the established line was negative for both cell surface and cytoplasmic immunoglobulin (Ig) chains. Absence of Ig expression was confirmed by Western blotting. Southern blot analysis demonstrated homozygous deletion of the C kappa gene, germ line configuration of the C lambda and rearrangement of IgJH genes. Cytogenetic analysis of both leukemic bone marrow and BALM-16 cells showed the t(8;22)(q24;q11) abnormality which is specifically associated with ALL-L3 and Burkitt lymphoma. The patient's serum showed hypercalcemia, prompting further investigation of the established cell lines which showed parathyroid hormone-related peptide (PTHrP) mRNA detected by reverse-transcriptase polymerase chain reaction. However, PTHrP production was not detected in the culture supernatant. The established cell line, BALM-16, could provide a useful material for analyzing the lack of Ig expression and of clarifying the pathogenesis of this type of B cell malignancy.

Effects of passive immunization against parathyroid hormone-related protein: PTHrP is the responsible factor in mediating hypercalcemia in the Walker carcinosarcoma 256 rat model

The Walker carcinosarcoma (WCS) 256 is a well-characterized rat model of humoral hypercalcemia of malignancy (HHM). We addressed the question of whether parathyroid hormone-related protein (PTHrP) is the factor responsible for mediating HHM in this model. WCS 256 cells were subcutaneously implanted in female rats. We examined the plasma at days 0, 2, 4, 6, and 8. The midregional PTHrP measured by radioimmunoassay (RIA) and the plasma calcium increased significantly. Measuring PTHrP by a two-site immunoradiometric assay (IRMA) showed comparable results. There was a strong positive correlation between plasma calcium and midregional PTHrP (r = 0.85, p < 0.0001). A strong positive correlation between tumor weight and both midregional PTHrP (r = 0.83, p < 0.0001) and plasma calcium (r = 0.87, p < 0.0001) was also found. After surgical removal of the tumor at day 5, both plasma calcium and plasma PTHrP levels fell to within the normal range. Ip administration of native polyclonal antiserum against PTHrP(53-84) led to a significant decrease of plasma calcium. Extracted WCS 256 tumor showed 5-fold increased levels of midregional PTHrP compared with liver. Immunohistochemistry and Western blot were positive for PTHrP. RNA from the WCS 256 tumor was positive for PTHrP whereas liver tissue RNA was negative. WCS 256 cells grown in vitro also secreted PTHrP into the medium. We conclude that PTHrP is synthesized and secreted by WCS 256 and that PTHrP is the factor responsible for mediating hypercalcemia in the WCS 256 rat model.

Malignant phaeochromocytoma and hypercalcaemia

We describe a case of hypercalcaemia secondary to recurrent malignant phaeochromocytoma. Parathyroid-related protein (PTHrp 1-86) immunoreactivity was identified in plasma and PTHrp was identified by immunocytochemistry in tumour tissue.

[Malignant humoral hypercalcemia and the parathyroid hormone related protein]

Humoral hypercalcemia in malignant disease results from the production of humoral factors that act on bone to demineralize the skeleton, with subsequent release of calcium. It is characteristic of certain tumours without bony metastases. A recently discovered parathyroid hormone-related protein (PTHrP) has been implicated as a causative hypercalcemic agent. PTHrP exerts its calcium-mobilizing effects by interaction with parathyroid hormone (PTH) receptors in bone and kidney through its amino-terminal sequence, which is homologous with that of PTH. The human PTHrP gene could encode multiple isoforms of the protein due to alternative exon usage. Apart from its involvement in humoral hypercalcemia of malignancy, PTHrP has also been identified in normal tissues, such as keratinocytes and placenta, and is present in high concentration in milk. PTHrP may modulate the calcium homeostasis in some normal physiological conditions, probably acting in a paracrine fashion.

Humoral hypercalcemia of malignancy

Studies on humoral hypercalcemia of malignancy have shown that tumors produce a protein that acts through the parathyroid hormone (PTH) receptor but is immunologically distinct from PTH. We have recently purified and cloned a parathyroid hormone-related protein (PTHrP) from a human lung cancer cell line. Full length cDNA clones were isolated and found to encode a prepropeptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino terminal residues are identical with human PTH, although antisera directed at the amino terminus of PTHrP do not recognize PTH. A 34-amino acid synthetic peptide, PTHrP(1-34), was several times more potent than bovine or human PTH(1-34) in bioassays promoting the formation of cAMP and plasminogen activity in osteogenic sarcoma cells and activation of adenylate cyclase in chick kidney membranes. PTHrP(1-34) was also more potent than PTH(1-34) in stimulating cAMP and phosphate excretion and reducing calcium excretion in the isolated perfused rat kidney. PTHrP has been consistently demonstrated by immunohistochemistry in squamous cell carcinomas and in keratinocytes present in normal skin, but not in normal or hyperplastic parathyroid tissues or other tumors. PTHrP-like activity has been extracted from ovine placenta and fetal parathyroid tissue, suggesting that PTHrP may play a role in fetal calcium homeostasis.

Hypercalcemia and vitamin D metabolism in Hodgkin's disease. Is there an underlying immunoregulatory relationship?

Hypercalcemia is not common in Hodgkin's disease, but in reported cases is often unassociated with bone involvement. A case is presented demonstrating a mechanism involving elevated levels of 1,25-dihydroxy vitamin D3 (calcitriol). Similar cases in the literature are reviewed. Data implicating calcitriol as a hematolymphoid regulatory hormone are discussed as they may relate to lymphomas, leukemias, and paraneoplastic lymphocyte and monocyte/macrophage activity.

Parathyroid hormone-related protein: isolation, molecular cloning, and mechanism of action

Many factors, such as interleukin 1, TGF alpha, tumor necrosis factor alpha and beta, and PGs, have been implicated in etiological roles in HHM (Martin and Mundy, 1987). Much interest in the past has also centered upon the likelihood of ectopic secretion of PTH in this condition. We have purified a protein (PTHrP) implicated in HHM from a human lung cancer cell line (BEN). Full-length cDNA clones have been isolated and were found to encode a prepropeptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino acids were identical with human PTH, although antisera directed to the NH2 terminus of PTHrP do not recognize PTH; this homology is not maintained in the remainder of the molecule. PTHrP therefore represents a previously unrecognized hormone, possibly related to the PTH gene by a gene duplication mechanism. In support of this notion, the PTHrP gene has been localized to the short arm of chromosome 12; it is believed that chromosome 11, containing the PTH gene, and chromosome 12 are evolutionarily related. In addition, the human PTHrP gene has been isolated, characterized, and shown to have a similar intron--exon organization as the PTH gene. It is possible that the original ancestral gene is indeed the PTHrP gene; resolution of this question awaits studies in lower species. Peptides synthesized to the predicted protein sequence have enabled detailed structure-function studies that have identified NH 2-terminal sequences to be responsible for the biological effects of the molecule. Antibodies raised against the various synthetic peptides have led to the immunohistochemical localization of PTHrP in many human squamous cell carcinomas as well as in a subpopulation of keratinocytes of normal skin. The availability of these antibodies has opened the way for the development of a radioimmunoassay to detect PTHrP in the sera of cancer patients at risk of developing hypercalcemia. The recent characterization of PTHrP-like activity in the ovine fetus suggests some physiological function for PTHrP. It is possible that PTHrP, as the fetal counterpart of PTH, has the role of maintaining the maternal-fetal calcium gradient. The isolation and characterization of PTHrP have added to our understanding of the mechanisms of hypercalcemia and may contribute to the understanding of other metabolic bone diseases, such as osteoporosis and Paget's disease. Finally, and perhaps most importantly, PTHrP may play a hitherto unrecognized role in normal cell physiology.

Defective host defence mechanisms in a family with hypocalciuric hypercalcaemia and coexisting interstitial lung disease

An extensive in vitro investigation of the host defence system was performed in 11 sibs of a large kindred with unexplained combination of familial hypocalciuric hypercalcaemia (FHH), interstitial lung disease and increased susceptibility to respiratory infections. The impairment of host defence mechanism was most likely related to granulocyte dysfunction. A severe myeloperoxidase deficiency was the most consistent granulocyte defect (P less than 0.001) and it was associated with a relatively diminished chemiluminescence (P less than 0.001). Moreover, a significantly diminished antistaphylococcal phagocytic (P less than 0.001) and killing (P less than 0.001) activity was found which in the absence of any opsonizing defect implicates an intrinsic granulocyte dysfunction. We found no abnormalities in number of B and T lymphocytes nor in the balance between helper and suppressor cells determined with monoclonal antibodies. Despite the recurrent infections no elevations of the immunoglobulin subclasses were found. The relationship between the inherited FHH, interstitial lung disease and susceptibility to respiratory infections remains obscure. It is, however, clear that impairment of the host defence might contribute to a decreased life expectancy in this family.

HLA antigens and familial benign hypercalcaemia

We have determined the blood groups and HLA haplotypes in 15 members in four generations of a large kindred with familial benign hypercalcaemia (familial hypocalciuric hypercalcaemia). No linkage was seen between the disorder and ABO or Rh blood groups or the HLA antigens.

Alterations of immunoreactive somatostatin in thyroid C cells after induced hypercalcemia, hypocalcemia, and antithyroid drug treatment

In order to elucidate the functional significance of somatostatin in thyroid C cells, the alterations of immunoreactive somatostatin in the cells were investigated under various experimental conditions, i.e., hypercalcemia, hypocalcemia, and antithyroid drug treatment. Guinea pigs and rabbits, in which almost all C cells reveal the intense immunoreaction for somatostatin in addition to calcitonin, were used as experimental animals. After chronically induced hypercalcemia, somatostatin immunoreactivity conspicuously diminished coinciding with the decrease of calcitonin; somatostatin as well as calcitonin was responsive to induced hypercalcemia. After hypocalcemic tetany induced by injection of Escherichia coli L-asparaginase, C cells exhibited very intense immunoreactions for both calcitonin and somatostatin. After chronic treatment of ethylenethiourea, immunoreaction of somatostatin in C cells was the same as that of calcitonin. That is, when immunoreactivity for calcitonin remained unchanged, immunoreactivity for somatostatin was also intensive. However, when immunoreaction of calcitonin became very weak, the reaction of somatostatin was also weak. Thus, in all experimental conditions examined the alterations of immunoreactive somatostatin in C cells completely coincided with those of calcitonin. It seems likely that somatostatin in thyroid C cells exerts the synergistic effect on calcitonin action.

Mechanisms of hypercalcemia in patients with head and neck cancer

Hypercalcemia associated with head and neck malignancy is not an uncommon occurrence; its causes are multiple. Eight hypercalcemic patients with head and neck malignancy were studied. Serum calcium, serum phosphorus, tubular phosphorus threshold, fasting calcium excretion, plasma 1,25-dihydroxyvitamin D, nephrogenous cyclic adenosine monophosphate (AMP), and immunoreactive parathyroid hormone were measured. Excessive dietary calcium administration in the form of an oral hyperalimentation preparation appeared to be the cause of hypercalcemia in 2 patients. Six patients demonstrated humorally mediated hypercalcemia. These patients resembled patients with primary hyperparathyroidism in having elevated nephrogenous cyclic AMP excretion and reduced proximal tubular phosphorus reabsorption, but they differed from patients with primary hyperparathyroidism by having normal levels of immunoreactive parathyroid hormone, markedly increased fasting calcium excretion, and strikingly reduced mean plasma levels of 1,25-dihydroxyvitamin D. These data strongly suggest that the humoral factor responsible for hypercalcemia in patients with head and neck cancer is not parathyroid hormone, and that patients with hyperparathyroidism can now be distinguished with confidence from those with malignancy-associated hypercalcemia.

Monoclonal rheumatoid factor (IgG lambda) its association with amyloid deposits containing lambda light chains

A patient with monoclonal IgG lambda rheumatoid factor was observed over a period of four years. During this time, serum level of the monoclonal protein fluctuated around 150 mg/dL and homogeneous lambda light chains were present in the urine. The patient died of squamous-cell carcinoma of the lung and no evidence of multiple myeloma was present at the time of autopsy. However, the patient had systemic amyloidosis that affected primarily the blood vessels in most organs. Both the vascular and parenchymal amyloid deposits stained for lambda light chains by the immunoperoxidase technique. These data support the hypothesis that amyloidogenic monoclonal immunoglobulins may be autoantibodies.

A calcium binding IgG myeloma protein

A calcium binding IgG was isolated and purified by column chromatography from serum of a myeloma patient with asymptomatic hypercalcaemia. The myeloma IgG, characterized as an IgG kappa, revealed a normal sized heavy chain (56 000 dalton), and a light chain of 31 000 dalton. Another population of IgG separated and purified from the same patient's serum did not bind calcium and had a normal 26 000 dalton light chain. Calcium binding activity in vitro is optimal at pH 8.0, and reaches its maximum after 3 h of 45Ca myeloma IgG incubation. Cleavage of the purified IgG by trypsin yielded peptides which were further isolated by column chromatography and characterized as Fab and Fc fragments. Light and heavy chains were obtained by reacting the immunoglobulin with dithiothreitol and iodoacetamide followed by Sephadex G-100 chromatography. Calcium binding activity was proved to be associated with Fab IgG fragment. Preparates containing Fc, heavy or light chains did not bind calcium in vitro.

Immuno-heterogeneity of the calcitonins of hypercalcemia, breast and lung cancers and medullary carcinoma of thyroid

Four antisera raised in the goat have very different properties: all recognized the immunoreactive calcitonin (iCT) of medullary carcinoma of the thyroid (MCT), one the response of normal subjects to induced or endogenous hypercalcemia and 2 others a different molecular species which occurs in half the patients with cancer of breast and 3/4 of patients with cancer of the lung. The latter two antisera are most sensitive to the 22-32 sequence of human calcitonin. Depending on the antiserum used, 4 or 7 peaks of immunoreactivity are found in eluates by column chromatography or stimulated serum from MCT. Not all elevated levels of iCT in serum are diagnostic of MCT and ectopic production by lung and breast cancer must be considered. Presence of higher levels of iCT with greater amounts of cancer tissue and undetectable levels after surgery or radiotherapy when using antisera which require intact molecule of calcitonin for recognition suggest the possibility that sequential calcitonin levels with differentiating antisera may be helpful in assessing the extent of disease and response to therapy.

Parathyroid hormone secretion in vivo. Demonstration of a calcium-independent nonsuppressible component of secretion

The response of normal bovine parathyroid glands to hypercalcemia was assessed in vivo by radioimmunoassay of immunoreactive parathyroid hormone concentrations in parathyroid effluent blood obtained by surgical cannulation of both anesthetized and nonanesthetized calves. Hypercalcemia was induced for periods of 0.3-35 h by intravenous infusion of a solution of calcium chloride. Assessment of immunoreactivity in effluent and peripheral blood included measurements of selected samples by use of a radioimmunoassay specific for a site residing in the biologically active portion of the hormone molecule. In all instances, the concentration of immunoreactive parathyroid hormone in hypercalcemic venous effluent from a superior parathyroid gland exceeded that of the peripheral blood. Failure of hypercalcemia to suppress completely secretion by normal parathyroids indicates that a portion of parathyroid hormone secretion occurs independent of blood calcium concentration. Consequently, continued parathyroid hormone secretion despite hypercalcemia can no longer be regarded as a unique feature of parathyroid neoplasia.

Immunoreactive forms of circulating parathyroid hormone in primary and ectopic hyperparathyroidism

The immunoreactive forms of parathyroid hormone (iPTH) in the plasma of six patients with primary, adenomatous hyperparathyroidism and six patients with ectopic hyperparathyroidism due to non-parathyroid cancer were compared by using gel filtration on columns of Bio-Gel P-150 and radioimmunoassay of iPTH in eluted fractions after concentration. We found much less (p<0.001) small (mol wt<9,500) COOH-terminal fragments of iPTH in plasma samples from ectopic hyperparathyroid patients (0.52+/-0.13 ng eq/ml) than in samples from primary hyperparathyroid patients (3.70+/-1.15 ng eq/ml). The quantity of iPTH eluting with or before native bovine PTH [1-84] was the same in both syndromes (ectopic hyperparathyroidism, 0.82+/-0.22 ng eq/ml; primary hyperparathyroidism, 0.73+/-0.09 ng eq/ml), and these values correlated positively with plasma calcium concentration (ectopic hyperparathyroidism, r=0.908; primary hyperparathyroidism, r=0.919). In both syndromes, plasma samples had an iPTH component that eluted well before PTH [1-84] (mol wt 9,500), but this component was present in much larger quantities in three patients with ectopic hyperparathyroidism. We conclude that (a) the decreased quantity of biologically inactive COOH-terminal fragments of iPTH circulating in ectopic hyperparathyroidism accounts for the previously reported relatively lower total serum iPTH values in this syndrome as compared with primary hyperparathyroidism (Riggs et al. 1971. J. Clin. Invest. 50: 2079); (b) there appears to be sufficient iPTH with presumed biologic activity to account for the hypercalcemia in both syndromes; (c) a large PTH component, not previously recognized in plasma, is present in both ectopic and primary hyperparathyroidism and may exist as the predominant immunoreactive form of the hormone in some patients with ectopic hyperparathyroidism.