High microsatellite instability (MSI-H) is associated with distinct clinical and molecular characteristics and an improved survival in early Colon cancer (CC); real world data from the AIO molecular registry Colopredict Plus

Colorectal cancer is one of the leading malignancies and still accounts for almost 25 000 deaths in Germany each year. Although there is accumulating data on the molecular basis, treatment and clinical outcome of patients within clinical trials evidence from the real-world setting is mostly lacking. We started the molecular registry trial Colopredict Plus in 2013 to collect clinical and molecular data from a real-world cohort of patients with early colon cancer stage II and III in 70 German colon cancer centers focusing on the prognostic impact of high microsatellite instability. In this interim report, we characterize a clinical cohort of 2615 patients, of whom 1787 tissue probes were analyzed. Microsatellite status was assessed using immunhistochemistry and fragment length analysis, with a concordance of 91.4 %. These established histopathological methods are sensitive and cost-effective. The median age was 72 years, significantly higher compared to clinical trial populations, with a median Charlson Comorbidity Index of 3. The stage-dependent incidence of microsatellite instability was 23.7 % and was associated with female gender, BRAF-mutation, UICC stage II and localization in the right colon. Survival calculated in disease free, relapse free and overall survival significantly differed between MSI-H and MSS, in favor of MSI-H patients. Multivariate age-adjusted analyses of relapse-free survival, disease-free survival, and overall survival highlighted microsatellite instability as a robust and positive prognostic marker for early colon cancer independent of age.

Baseline and interim PET-based outcome prediction in peripheral T-cell lymphoma: A subgroup analysis of the PETAL trial

The prospective randomized Positron Emission Tomography (PET)-Guided Therapy of Aggressive Non-Hodgkin Lymphomas (PETAL) trial was designed to test the ability of interim PET (iPET) to direct therapy. As reported previously, outcome remained unaffected by iPET-based treatment changes. In this subgroup analysis, we studied the prognostic value of baseline total metabolic tumor volume (TMTV) and iPET response in 76 patients with T-cell lymphoma. TMTV was measured using the 41% maximum standardized uptake value (SUV_41max ) and SUV₄ thresholding methods. Interim PET was performed after two treatment cycles and evaluated using the ΔSUV_max approach and the Deauville scale. Because of significant differences in outcome, patients with anaplastic lymphoma kinase (ALK)-positive lymphoma were analyzed separately from patients with ALK-negative lymphoma. In the latter, TMTV was statistically significantly correlated with progression-free survival, with thresholds best dichotomizing the population, of 232 cm³ using SUV_41max and 460 cm³ using SUV₄ . For iPET response, the respective thresholds were 46.9% SUV_max reduction and Deauville score 1-4 vs 5. The proportion of poor prognosis patients was 46% and 29% for TMTV by SUV_41max and SUV₄ , and 29% and 25% for iPET response by ΔSUV_max and Deauville, respectively. At diagnosis, the hazard ratio (95% confidence interval) for poor prognosis vs good prognosis patients according to TMTV was 2.291 (1.135-4.624) for SUV_41max and 3.206 (1.524-6.743) for SUV₄ . At iPET, it was 3.910 (1.891-8.087) for ΔSUV_max and 4.371 (2.079-9.187) for Deauville. On multivariable analysis, only TMTV and iPET response independently predicted survival. Patients with high baseline TMTV and poor iPET response (22% of the population) invariably progressed or died within the first year (hazard ratio, 9.031 [3.651-22.336]). Due to small numbers and events, PET did not predict survival in ALK-positive lymphoma. Baseline TMTV and iPET response are promising tools to select patients with ALK-negative T-cell lymphoma for early allogeneic transplantation or innovative therapies.

Hämorrhagisch-ulzeröser Verlauf einer eosinophilen Gastritis bei einem 79 Jahre alten Mann

Die eosinophile gastrointestinale Erkrankung (EGID) ist ein seltenes Krankheitsbild weitgehend unklarer Ätiologie. Wir beschreiben im Folgenden den Fall eines 79-jährigen Patienten mit der Erstdiagnose einer eosinophilen Gastritis mit hämorrhagisch-ulzerösem Verlauf und einer raschen Rekurrenz der Erkrankung nach Absetzen der medikamentösen Therapie.

Anamnese und klinischer Befund Der Patient gab an, seit mehreren Tagen Teerstuhl abzuführen. Zum Aufnahmezeitpunkt war der Patient beschwerdefrei. Die bestehende Medikation wurde in letzter Zeit nicht verändert.

Untersuchungen und Diagnose Gastroskopisch, endosonografisch und im CT fand sich ein malignitätsverdächtiger Tumor im Corpus ventriculi. Erst die histopathologische Untersuchung lieferte die korrekte Diagnose.

Therapie und Verlauf Der Patient wurde mit Prednisolon und PPI behandelt. Hierunter kam es zu einer Regredienz des Befundes und einer klinischen Vollremission. Ein Auslassversuch führte kurze Zeit später zu einem fulminanten Rezidiv. Nach Wiederaufnahme der medikamentösen Therapie war das erneut nachgewiesene gastrale Ulkus rasch rückläufig.

Folgerung Die EGID ist vom klinischen Erscheinungsbild her kaum zu identifizieren. Zur Diagnosestellung bedarf es einer histopathologischen Begutachtung. In der Behandlung spielen vor allem orale Glukokortikoide eine Rolle. Es sind sowohl Einzelepisoden als auch chronisch-rezidivierende Verläufe beobachtet worden. Die zur Therapie eingesetzten Medikamente sollten daher nur vorsichtig und unter regelmäßiger Befundkontrolle ausgeschlichen werden.

Sequential high-dose cytarabine and mitoxantrone (S-HAM) versus standard double induction in acute myeloid leukemia-a phase 3 study

Dose-dense induction with the S-HAM regimen was compared to standard double induction therapy in adult patients with newly diagnosed acute myeloid leukemia. Patients were centrally randomized (1:1) between S-HAM (2nd chemotherapy cycle starting on day 8 = “dose-dense”) and double induction with TAD-HAM or HAM(-HAM) (2nd cycle starting on day 21 = “standard”). 387 evaluable patients were randomly assigned to S-HAM (N = 203) and to standard double induction (N = 184). The primary endpoint overall response rate (ORR) consisting of complete remission (CR) and incomplete remission (CR_i) was not significantly different (P = 0.202) between S-HAM (77%) and double induction (72%). The median overall survival was 35 months after S-HAM and 25 months after double induction (P = 0.323). Duration of critical leukopenia was significantly reduced after S-HAM (median 29 days) versus double induction (median 44 days)—P < 0.001. This translated into a significantly shortened duration of hospitalization after S-HAM (median 37 days) as compared to standard induction (median 49 days)—P < 0.001. In conclusion, dose-dense induction therapy with the S-HAM regimen shows favorable trends but no significant differences in ORR and OS compared to standard double induction. S-HAM significantly shortens critical leukopenia and the duration of hospitalization by 2 weeks.

Association of microsatellite instability with distinct clinical and molecular characteristics in resected colon cancer: Analysis of a platform trial of the AIO colorectal study group—Colopredict Plus

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Background: High microsatellite instability (MSI-H) is a prognostic marker in resected colon cancer (CC) identified in post-hoc analysis of multiple trials. However, validation in real-life cohorts and its association with clinical and molecular markers is lacking. Methods: In Sep 2013 we started a platform trial in 49 German cancer centers recruiting patients with UICC stage II and III CC diagnosed between 2008 to 2016. MSI was tested by immunohistochemistry (IHC) of mismatch repair proteins MLH1, MSH2, MSH6 and PMS2. In case of any loss of protein expression (IHC neg), fragment length analysis (FLA) was performed, defining MSI high tumors (MSI-H) and MS stable tumors (MSS). Besides, mutations in known prognostic factors for CC such as RAS, BRAF, PI3K and others were determined by next generation sequencing (NGS). Results: By end of 2016, 1249 patients have been recruited into the trial: median age 73yrs., stage II/III: 686/563 pts. So far, tissue was analysed in 512 pts. Of these, 182 pts. were IHC neg with 116 pts. tested MSI-H upon FLA (22.7%). Median age was 73yrs., female/male: 260/252 pts., stageII/III: 292/220 pts. Association of MS status with clinical factors is shown in Table 1. Upon NGS analysis we found 16.3% BRAF mutations, 39% KRAS mutations, 2.8% NRAS mutations and 22.6% PI3K mutations. MSI-H status was significantly associated with BRAF mutation and wildtype status of RAS. Conclusions: We found a higher percentage of MSI-H cancers in our registry compared to reported data from randomised trials, possibly related to a higher median age in this real-life cohort. MSI-H was associated with female sex, primary tumor site, and distinct molecular markers and should therefore be considered a heterogeneous subgroup of CC. Updated analysis including NGS data and survival will be presented at the meeting. Clinical trial information: AIO- KRK-0413, DKRS:00004305. [Table: see text]

Comparing long-term toxicity and efficacy of combined modality treatment including extended- or involved-field radiotherapy in early-stage Hodgkin's lymphoma

BACKGROUND

To evaluate long-term toxicity and efficacy of a combined modality strategy including extended-field radiotherapy (EF-RT) or involved-field radiotherapy (IF-RT), the German Hodgkin Study Group carried out a follow-up analysis in patients with early unfavorable Hodgkin's lymphoma (HL).

PATIENTS AND METHODS

One thousand two hundred and four patients were randomized to four cycles of chemotherapy followed by either 30 Gy EF- or 30 Gy IF-RT (HD8 trial); 532 patients in each treatment arm were eligible.

RESULTS

At 10 years, no arm differences were revealed with respect to freedom from treatment failure (FFTF) (79.8% versus 79.7%), progression-free survival (79.8% versus 80.0%), and overall survival (86.4% versus 87.3%). Non-inferiority of IF-RT was demonstrated for the primary end point FFTF (95% confidence interval for hazard ratio 0.72-1.25). Elderly patients had a poorer outcome when treated with EF-RT. So far, 15.0% of patients in arm A and 12.2% in arm B died, mostly due to secondary malignancies (5.3% versus 3.4%) or HL (3.2% versus 3.4%). After EF-RT, there were more secondary malignancies overall (58 versus 45), especially acute myeloid leukemias (11 versus 4).

CONCLUSION

Radiotherapy intensity reduction to IF-RT does not result in poorer long-term outcome but is associated with less acute toxicity and might be associated with less secondary malignancies.

Poorer outcome of elderly patients treated with extended-field radiotherapy compared with involved-field radiotherapy after chemotherapy for Hodgkin's lymphoma: an analysis from the German Hodgkin Study Group

BACKGROUND

The optimal treatment of elderly patients with Hodgkin's lymphoma (HL) is still a matter of debate. Since many of these patients receive combined modality treatment, we evaluated the impact of different radiation field sizes, that is extended-field (EF) or involved-field (IF) technique when given after four cycles of chemotherapy.

PATIENTS AND METHODS

In the multicenter HD8 study of the German Hodgkin Study Group, 1204 patients with early-stage unfavorable HL were randomized to receive four cycles of chemotherapy followed by either radiotherapy (RT) of 30 Gy EF + 10 Gy to bulky disease (arm A) or 30 Gy IF + 10 Gy to bulky disease (arm B). A total of 1064 patients were assessable for the analysis. Of these, 89 patients (8.4%) were 60 years or older.

RESULTS

Elderly patients had a poorer risk profile. Acute toxicity from RT was more pronounced in elderly patients receiving EF-RT compared with IF-RT [World Health Organization (WHO) grade 3/4: 26.5% versus 8.6%)]. Freedom from treatment failure (FFTF, 64% versus 87%) and overall survival (OS, 70% versus 94%) after 5 years was lower in elderly patients compared with younger patients. Importantly, elderly patients had poorer outcome when treated with EF-RT compared with IF-RT in terms of FFTF (58% versus 70%; P = 0.034) and OS (59% versus 81%; P = 0.008).

CONCLUSION

Elderly patients with early-stage unfavorable HL generally have a poorer risk profile and outcome when compared with younger patients. Treatment with EF-RT instead of IF-RT after chemotherapy has a negative impact on survival of elderly patients and should be avoided.

Acute myeloid leukemia (AML) with t(8;21)(q22;q22) relapsing as AML with t(3;21)(q26;q22)

We here report on an 48-year-old male patient with a primary diagnosis of acute myeloid leukemia (AML)-M2 with t(8;21)(q22;q22), who developed complete hematologic and molecular remission after induction chemotherapy. Thirteen months later, he relapsed and showed an AML-M2 with t(3;21)(q26;q22). Retrospectively, polymerase chain reaction (PCR) for AML1-EVI1 and EVI1 overexpression was performed on bone marrow and peripheral blood samples taken at diagnosis and during the first year after the first manifestation of AML to quantify the AML1-EVI1-positive clone. In a bone marrow sample taken 25 days from diagnosis, PCR for AML1-EVI1 was negative, and EVI1 expression, as assessed by quantitative real-time PCR, was within the same range as that of healthy controls. These data suggest that this patient developed a secondary therapy-related AML rather than a relapse.

[Echinococcosis - a rare differential diagnosis of a tumorous hepatic lesion]

We report the case of a 44-year-old woman who was admitted to our hospital because of a newly developed painless jaundice. Though she felt quite well sonographic and radiographic evaluation showed a tumor of the liver. An extensive diagnostic workup was performed but it was not until laparotomy that a malignant tumor could definitely be ruled out and the presumptive diagnosis of an echinococcosis was proven. A partial resection of the liver was performed.

Extranodal mantle cell lymphoma mimicking marginal zone cell lymphoma

AIM

We report a case of mantle cell lymphoma masquerading as a marginal zone cell lymphoma.

METHODS AND RESULTS

In the initial manifestation in the palatine tonsils, the neoplastic cells were found to grow exclusively within the marginal zones of secondary follicles which showed a preserved mantle zone. The few immunostains performed showed a B-cell phenotype including an immunoglobulin light chain restriction. The extranodal manifestation, the growth pattern, and the immunophenotype led to the diagnosis of an extranodal marginal zone B-cell non-Hodgkin's lymphoma (NHL). The specimen from the relapse occurring 8 months later exhibited diffuse monomorphous cells co-expressing B-cell antigens and CD5, CD43 and cyclin D1, leading to the diagnosis of mantle cell lymphoma. Re-investigation of the initial biopsy revealed that the neoplastic cells within the marginal zones had a mantle cell lymphoma immunophenotype expressing cyclin D1, the immunoglobulin heavy chains IgD and IgM and partly CD5. Both lesions harboured identical clonal immunoglobulin gene rearrangements proving that they represented different manifestations of the same lymphoma.

CONCLUSION

This case emphasizes the importance of broad immunohistological investigation of B-cell NHLs involving the marginal zone.

[Transesophageal endosonographically-guided fine needle aspiration biopsy of mediastinal space-occupying lesions of uncertain importance]

BACKGROUND AND OBJECTIVE

Endoscope-guided fine-needle biopsy of mediastinal space-occupying lesions is a recently introduced method of low invasiveness. This is a report of the authors' experience.

PATIENTS AND METHODS

Between Nov. 1996 and April 1999 endoscope-guided mediastinal biopsies (Pentax FG 32 UA) were performed in 31 patients (eight women, 23 men; aged 27-80 years). The space-occupying lesion had to be less than 1 cm from the oesophagus and not more easily approachable in other ways.

RESULTS

The method was successful in 23 of the 31 patients (74%). In ten of the 31 patients (32%) a malignant lesion was histologically proven. In six patients (19%) sarcoidosis was revealed. Of the eight patients with inadequate biopsy material a malignancy was ultimately diagnosed in three, sarcoidosis in one (in three by mediastinoscopy, in one by laparoscopy). Thus the sensitivity of diagnosing a malignancy was 77%, with a specificity of 100%. Follow-up examinations in the remaining four patients excluded a malignancy.

CONCLUSION

Endoscope-guided fine-needle biopsy of mediastinal space-occupying lesions is a technically simple method causing little stress to the patient that can frequently elucidate the lesion's benignity or malignancy. Invasive procedures, such as mediastinoscopy, may thus be avoided in some patients.

Induction of a graft-versus-leukemia reaction by cyclosporin A withdrawal as immunotherapy for leukemia relapsing after allogeneic bone marrow transplantation

We studied the immunomodulating effect of withdrawal of immunosuppression with cyclosporin A (CsA) in 42 patients with leukemic relapse of chronic myelogenous leukemia (CML) (n = 24), acute myeloid leukemia (AML) (n = 13) and acute lymphoblastic leukemia (ALL) (n = 5) after allogeneic unmanipulated bone marrow (BMT) or peripheral blood stem cell transplantation (PBSCT). Response to CsA withdrawal was monitored molecularly by the polymerase chain reaction for elimination of CML cells containing the bcr-abl messenger RNA (mRNA) transcript (n = 24), or mll-af4 mRNA transcript characteristic of leukemic cells with a 11q23 chromosomal abnormality (n = 1). Rapid tapering of CsA resulted in subsequent achievement of cytogenetic remission in 11 of 14 CML patients (79%) who relapsed in early disease phase (n = 9 cytogenetic relapse, n = 2 hematological relapse) after a median of 57 days. Three of 13 AML patients and one of five ALL patients achieved complete remission. CsA withdrawal was accompanied by the development of acute graft-versus-host disease (GVHD) grade II in most of the 24 patients with CML. Two patients who achieved remission of AML or ALL died from severe GVHD grade III-IV. We calculated a probability of 84% for achieving and remaining in remission with early relapse of CML 4 years after relapse post BMT, whereas patients with AML have only a probability of about 10% of achieving and remaining in remission after 3 years. Patients with advanced CML and ALL had no chance of achieving and remaining in remission in the same time period.

[Granulomatous hepatitis and myelitis: an unusual manifestation of extrapulmonary sarcoidosis]

Sarcoidosis is a chronic multisystem disorder of unknown cause characterized by the presence of noncaseating epitheloid granulomas and derangement of the normal skin architecture. Though an array of organs may be affected by the disease the most common site of affection is the lung. An extrathoratic manifestation is rare. We describe a 66-year-old patient who was admitted to our hospital because of weight loss and hepatomegaly. A thorough examination revealed the diagnosis of a granulomatous hepatitis characterized by a markedly elevated alkaline phosphatase concentration of 1,490 U/I. A drug-induced hepatitis could be excluded and no evidence was found for the existence of a bacterial or viral infection or an autoimmune disorder. An ERCP revealed a normal common bile duct and normally branching small intrahepatic ducts. The patient was discharged with the diagnosis of a biliary cirrhosis. Half a year later the patient was readmitted to the hospital because of severe intestinal bleeding due to pancytopenia. A bone marrow biopsy showed infiltration of the marrow by granulomas. A histiocytosis X could be ruled out. The diagnosis of an extrathoracic sarcoidosis was assumed and a therapy with prednisone was started. Within six weeks the blood count normalized. After 18 months the serum alkaline phospatase concentration also normalized and no granulomas were found in the bone marrow. The case demonstrates that pancytopenia in sarcoidosis is not due to bone marrow failure.

The clonal relationship between nodular sclerosis Hodgkin's disease with a clonal Reed-Sternberg cell population and a subsequent B-cell small noncleaved cell lymphoma

We evaluated the clonal relationship between a case of nodular sclerosis Hodgkin's disease (NSHD) and a small noncleaved cell (SNC) lymphoma that subsequently developed. Single Hodgkin and Reed-Sternberg (H-RS) cells were isolated from immunostained sections of the NSHD by micromanipulation, and the immunoglobulin heavy chain gene (IgH) complementarity determining region (CDR) III of the cells was amplified by the polymerase chain reaction (PCR). A clonal population of H-RS cells was found in the NSHD tumor. The nucleotide sequence of the clonal H-RS cells was compared with the clonal IgH CDRIII sequence from the SNC lymphoma. The two sequences were found to be unrelated. In addition, clone-specific primers and probes were designed from the two clonal IgH CDRIII sequences and used to investigate the presence of the respective clonal population in the NSHD tumor. The latter studies confirmed the presence of a major clonal H-RS cell population, as detected by the single cell assay, but cells corresponding to the SNC clone were not demonstrable by this highly sensitive technique. These findings suggest that the SNC arising in this case represents the development of the second neoplasm clonally unrelated to the preceding NSHD. They also support the recent findings that the H-RS cells in classical HD consist of a clonal population of B cells.

HIV-related non-Hodgkin's lymphoma: CHOP induction therapy and interferon-alpha-2b/zidovudine maintenance therapy

In a prospective multicenter study 68 out of 158 patients with HIV infection and malignant lymphoma were assigned to a risk-adapted induction therapy using the following algorithm: High-risk patients fulfilled 2 of 3 criteria: T4 lymphocytes <50/microL; WHO activity index 3 or 4; pre-existing AIDS-defining opportunistic infection. Normal-risk patients received 4 to 6 cycles of CHOP chemotherapy; those that achieved complete remission (CR) received zidovudine (500 mg/d) and interferon-alpha maintenance therapy (5 million units three times a week) for one year. High-risk patients received low-dose CHOP or vincristine/prednisone chemotherapy. Supportive care was performed with pentamidine inhalation and G-CSF. Intrathecal (it) methotrexate was given for CNS prophylaxis. The median survival was 634 days for 38 patients of the normal-risk group and 129 days for 30 patients of the high-risk group. 18 high-risk patients treated with low-dose CHOP had better survival (156 days) than 12 patients treated with vincristine/prednisone (72 days p=0.044). 68% of the patients in the normal-risk group achieved complete remission. 5 out of 18 high-risk patients treated with low-dose CHOP achieved complete remission. Three normal-risk patients developed fatal opportunistic infections during chemotherapy. Immune parameters deteriorated after CHOP induction and partially recovered with maintenance treatment. We conclude that the normal-risk patients survived longer than reported in most published studies. Toxicity was low. Low-dose CHOP seems to be superior to vincristine/prednisone therapy in high-risk patients.

Use of various diagnostic methods in a patient with Gaucher disease type I

A series of plain radiographs, bone scans, bone marrow scans, and MRIs is reported in a patient with Gaucher disease type I, in whom two episodes of acute bone crisis developed during a 6-year period of follow-up. Acute bone crisis and global indolent bone marrow displacement could both be assessed by bone marrow scintigraphy, whereas MRI could better clarify the corti-comedullary alteration after bone infarction. Thus, MRI and bone marrow scintigraphy could be used as complementary imaging methods in the management of patients with Gaucher disease.

Differential effect of the activation of protein kinase A on the protein synthesis and secretion in the T-helper 2 cell line D10.G4.1

The authors analysed the effect of protein kinase A (PKA) activation on the protein synthesis and secretion in the T-helper 2 cell line D10.G4.1 (D10) using an assay that allows the detection of almost all secreted proteins of a cell. IL-4 and IL-10 were quantified. Three groups of secretory products could be defined. The T-cell receptor (TCR)-induced production of the first group (A) of proteins including IL-4 was enhanced by low concentrations of PKA activators. At higher concentrations the enhancement was less marked. The synthesis and secretion of a second group (B) of proteins including IL-10 remained unaffected. The production of a third group (C) of proteins was inhibited in a concentration-dependent manner. Biochemical analysis revealed a block of phospholipase C gamma (PLC gamma) activity by PKA activators. When D10 cells were stimulated by a phorbol ester plus calcium ionophore the production of group A proteins was enhanced almost fourfold, whereas production of group B proteins was unaffected by PKA activation. This effect was observed at all concentrations of various PKA activators tested. The secretion of group C proteins was no longer inhibited. The same results were obtained when analysing IL-4 and IL-10 m-RNA by Northern blotting. The data demonstrate a lymphokine specific mode of action on a single cell basis. Furthermore, it suggests that the inhibitory action of PKA in D10 cells is due partly to blocking of PLC gamma activity.

Detection of distinct sets of newly synthesized polypeptides in supernatants of TCR-triggered T cell clones. Implication for the search for new lymphokines

Using metabolic radiolabelling of proteins, which are newly synthesized during TCR-triggered T cell activation we were able to visualize distinct patterns of secreted polypeptides (with molecular weights ranging from 6 to 44 kDa) in supernatants of different T helper-1, T helper-2 and cytotoxic T cell clones. Most of these detected proteins are secreted in response to TCR-crosslinking (or to combined action of PMA and A231287), in an extracellular Ca(2+)-dependent manner and their appearance in supernatants was completely blocked by the addition of RNA synthesis or protein synthesis inhibitors or EGTA. Cyclosporin A (CsA) blocks secretion of several detected polypeptides, but does not affect TCR-triggered synthesis and secretion of others reflecting the existence of TCR-triggered, CsA-insensitive protein synthesis and secretion pathway. The insensitivity of secretion of several easily detectable polypeptides to inhibition by CsA offers a promising approach to further define the CsA-resistant and calcineurin-independent molecular pathways of TCR-triggered T cell activation. Several lymphokines (e.g., interferon-gamma, tumor necrosis factor, interleukin-4 and interleukin-10) are identified among the visualized set of secreted polypeptides. Since other, yet unidentified, secreted polypeptides in the same set of secreted proteins share important properties with known lymphokines it seems promising to use described approach in search for new lymphokines.

Dissociation between phytohaemagglutinin-stimulated generation of inositol phosphates and Ca2+ increase in human mononuclear leucocytes

We have tested whether phytohaemagglutinin (PHA)-stimulated generation of inositol phosphates (IP) and increases in intracellular Ca2+ can be dissociated in human mononuclear leucocytes. Lowering the incubation temperature from 37 degrees to 25 degrees C decreased PHA-stimulated IP generation by more than 80%, but only marginally affected PHA-stimulated Ca2+ increases. In the absence of extracellular Ca2+, PHA did not stimulate IP generation or Ca2+ increases, although PHA binding to its acceptor sites was not impaired. Increasing extracellular Ca2+ up to 0.15 mM enhanced PHA-stimulated PHA generation but this increase was attenuated by further increasing extracellular Ca2+ to 2.6 mM. Increasing extracellular Ca2+ to 0.3 mM also enhanced PHA-stimulated Ca2+ increases, and further increasing extracellular Ca2+ did not affect it. Co-treatment with 100 microM-prostaglandin E2 completely abolished PHA-stimulated IP generation, but inhibited Ca2+ increases by only 20-30%. These results could be explained by IP-generation-independent Ca2+ increases or by non-linear coupling of IP generation to Ca2+ increases. Since the PHA concentrations required to increase Ca2+ were greater than those required for IP generation, the latter hypothesis can be excluded. Furthermore, the Ca2+ ionophore ionomycin increased intracellular Ca2+ and weakly stimulated IP generation, but with very similar concentration-response relationships. Our data suggest that PHA-stimulated IP generation and Ca2+ increases in human mononuclear leucocytes mainly occur independently of one another rather than sequentially.

Functional and biochemical characterization of a calcium-ionophore-induced state of unresponsiveness in a cytolytic T cell clone

To characterize the requirements for the induction of an anergic state in immunocompetent cells we examined the effect of an increase in intracellular calcium concentration on the subsequent responsiveness of cytolytic T cells to antigenic stimulation in vitro. Pretreatment of a murine cytolytic T cell clone with the calcium-ionophore A23187 resulted in the induction of an anergic state characterized by a decrease in cytolytic activity and granule exocytosis upon Ag-specific stimulation. Furthermore, IFN-gamma synthesis declined whereas de novo synthesis of a yet unidentified protein with a molecular mass of 33 kDa as well as proliferative response of cells in response to exogenous IL-2 were unaffected. This state of partial unresponsiveness 1) could be prevented by concomitant pretreatment of cells with cyclosporin A or protein synthesis inhibitors and 2) was reversible within 48 h. Biochemical analysis of TCR-induced intracellular activation revealed a block in signal transduction before the activation of protein kinase C because cellular unresponsiveness could be bypassed by the phorbol ester PMA plus the calcium-ionophore A23187. However, phosphatidylinositol turnover was markedly inhibited in unresponsive cells that also did not show a calcium influx on stimulation with concanavalin A. We conclude that a rise in intracellular calcium in cytolytic T cells might not only be necessary for cellular activation but may also trigger the induction of a partial unresponsiveness to antigenic stimulation due to an inhibition in the early phase of signal transduction.

Functional and biochemical characterization of a calcium-ionophore-induced state of unresponsiveness in a cytolytic T cell clone

To characterize the requirements for the induction of an anergic state in immunocompetent cells we examined the effect of an increase in intracellular calcium concentration on the subsequent responsiveness of cytolytic T cells to antigenic stimulation in vitro. Pretreatment of a murine cytolytic T cell clone with the calcium-ionophore A23187 resulted in the induction of an anergic state characterized by a decrease in cytolytic activity and granule exocytosis upon Ag-specific stimulation. Furthermore, IFN-gamma synthesis declined whereas de novo synthesis of a yet unidentified protein with a molecular mass of 33 kDa as well as proliferative response of cells in response to exogenous IL-2 were unaffected. This state of partial unresponsiveness 1) could be prevented by concomitant pretreatment of cells with cyclosporin A or protein synthesis inhibitors and 2) was reversible within 48 h. Biochemical analysis of TCR-induced intracellular activation revealed a block in signal transduction before the activation of protein kinase C because cellular unresponsiveness could be bypassed by the phorbol ester PMA plus the calcium-ionophore A23187. However, phosphatidylinositol turnover was markedly inhibited in unresponsive cells that also did not show a calcium influx on stimulation with concanavalin A. We conclude that a rise in intracellular calcium in cytolytic T cells might not only be necessary for cellular activation but may also trigger the induction of a partial unresponsiveness to antigenic stimulation due to an inhibition in the early phase of signal transduction.

Biochemical characterization of the inhibitory effect of CsA on cytolytic T lymphocyte effector functions

We have examined the effects of cyclosporine A (CsA) on a number of CTL effector functions. CsA partially inhibited the CTL-mediated lysis of Ag-bearing target cells. Both target cell- and anti-TCR mAb-induced granule exocytosis were markedly inhibited by CsA. In addition, marked inhibition of PMA and calcium ionophore (A23187) induced granule exocytosis was produced by CsA suggesting that the inhibitory effects of CsA on granule exocytosis involve biochemical events after protein kinase C activation and increases in intracellular free Ca2+. CsA had no inhibitory effects on TCR-mediated phosphatidylinositol metabolism. The inhibitory effects of CsA were not mediated by the cAMP-dependent protein kinase inhibitory pathway and no effect of CsA on the Ca2+-induced binding of calmodulin to calmodulin-binding proteins could be demonstrated. CsA was also a potent inhibitor of IgE receptor-mediated exocytosis in rat basophil leukemia cells. CsA had no effect on receptor-mediated phosphatidylinositol hydrolysis; 400 ng/ml CsA resulted in a 90% inhibition of serotonin release but had no effect on phosphatidylinositol hydrolysis. These results indicate that CsA may inhibit some common event in Ca2+-dependent secretory cells. Taken together, these results suggest that CsA does not inhibit signal transduction but rather interferes with the biochemical events in the later stages of Ca2+-dependent reactions that follow the binding of calmodulin to cytoskeletal or cytoplasmic calmodulin binding proteins.

Biochemical characterization of the inhibitory effect of CsA on cytolytic T lymphocyte effector functions

We have examined the effects of cyclosporine A (CsA) on a number of CTL effector functions. CsA partially inhibited the CTL-mediated lysis of Ag-bearing target cells. Both target cell- and anti-TCR mAb-induced granule exocytosis were markedly inhibited by CsA. In addition, marked inhibition of PMA and calcium ionophore (A23187) induced granule exocytosis was produced by CsA suggesting that the inhibitory effects of CsA on granule exocytosis involve biochemical events after protein kinase C activation and increases in intracellular free Ca2+. CsA had no inhibitory effects on TCR-mediated phosphatidylinositol metabolism. The inhibitory effects of CsA were not mediated by the cAMP-dependent protein kinase inhibitory pathway and no effect of CsA on the Ca2+-induced binding of calmodulin to calmodulin-binding proteins could be demonstrated. CsA was also a potent inhibitor of IgE receptor-mediated exocytosis in rat basophil leukemia cells. CsA had no effect on receptor-mediated phosphatidylinositol hydrolysis; 400 ng/ml CsA resulted in a 90% inhibition of serotonin release but had no effect on phosphatidylinositol hydrolysis. These results indicate that CsA may inhibit some common event in Ca2+-dependent secretory cells. Taken together, these results suggest that CsA does not inhibit signal transduction but rather interferes with the biochemical events in the later stages of Ca2+-dependent reactions that follow the binding of calmodulin to cytoskeletal or cytoplasmic calmodulin binding proteins.

Cyclic AMP-dependent protein kinase as a part of the possible down-regulating pathway in the antigen receptor-regulated cytotoxic T lymphocyte conjugate formation and granule exocytosis

Screening activities of cytotoxic T lymphocytes (CTL) are viewed as a cycle of engagements and disengagements with target cells. One of the unexplained features of CTL activation is a biochemical mechanism of an "off" signal, which would result in disengagement of CTL from the target cell and termination of exocytosis of granules. Data are presented that suggest that cAMP dependent-protein kinase (PK-A) inhibits both early and late stages of antigen receptor-regulated CTL activation and may be a part of such an off signaling pathway.

B cell stimulatory factor 1 (IL-4) enhances the development of cytotoxic T cells from Lyt-2+ resting murine T lymphocytes

B cell stimulatory factor 1 (BSF-1) (IL-4) was shown to synergize with phorbol esters or with monoclonal anti-TCR antibody in stimulation of the development of CTL from small resting murine T cells. IL-2 also synergized with PMA in such differentiation but was less effective than BSF-1. The combination of these two lymphokines with PMA had the most potent effect on the development of CTL. BSF-1 plus PMA stimulated a significant increase in the intracellular content of N-benzyloxycarbonyl-L-lysine thiobenzylester esterase, a granule-associated biochemical marker, whereas IL-2 plus PMA was only marginally effective. Depletion of L3T4+ cells did not result in the abrogation of these effects. Lyt-2+ T cells that were incubated for 72 h with BSF-1 plus PMA accumulated N-benzyloxycarbonyl-L-lysine thiobenzylester esterase and secreted this intragranular marker after interaction with immobilized anti-T cell receptor mAb. These BSF-1/PMA-stimulated Lyt-2+, L3T4- T cells were also able to kill FcR positive target cells in a retargeting assay with a mAb to murine T3 Ag, providing evidence that BSF-1 plus PMA acted directly on precursors of cytotoxic T cells.

Locus of inhibitory action of cAMP-dependent protein kinase in the antigen receptor-triggered cytotoxic T lymphocyte activation pathway

The mechanism of the cAMP involvement in regulation of cellular functions was studied here using a novel functional assay (antigen receptor-triggered exocytosis of granules) of cloned cytotoxic T lymphocytes (CTL). We suggest that cAMP-dependent protein kinase, protein kinase A, counteracts the protein kinase C and Ca2+-mediated stimulatory T-cell antigen receptor (TcR)-triggered biochemical pathway. This suggestion is supported by experimental results which satisfy criteria for protein kinase A involvement in cellular functions. Pretreatment of CTL with cholera toxin induces cAMP accumulation in CTL, partially inhibits TcR-triggered "lethal hit" delivery to the target cell, and almost completely blocks TcR-triggered exocytosis of granules from CTL. Other agents that raise the intracellular level of cAMP, including forskolin and isobutylmethylxanthine (IBMX) also inhibit TcR-triggered CTL activation. Involvement of cAMP-dependent protein kinase in an inhibitory pathway is suggested by the synergistic effects of cyclic nucleotide analogs 8-bromo-cAMP and N6-benzoyl-cAMP in inhibition of TcR-triggered exocytosis. Forskolin and IBMX inhibited TcR-triggered phosphoinositide turnover in CTL, suggesting that cAMP affected very early events in signal transduction that follow TcR cross-linking by a ligand. The ability of IBMX to inhibit CTL activation when the TcR cross-linking step was by-passed by the combination of phorbol myristate acetate and ionophore A23187 suggests that the locus of inhibitory effect of cAMP is at both the early and late stages of the TcR-triggered transmembrane signaling pathway.

B cell stimulatory factor 1 (IL-4) enhances the development of cytotoxic T cells from Lyt-2+ resting murine T lymphocytes

B cell stimulatory factor 1 (BSF-1) (IL-4) was shown to synergize with phorbol esters or with monoclonal anti-TCR antibody in stimulation of the development of CTL from small resting murine T cells. IL-2 also synergized with PMA in such differentiation but was less effective than BSF-1. The combination of these two lymphokines with PMA had the most potent effect on the development of CTL. BSF-1 plus PMA stimulated a significant increase in the intracellular content of N-benzyloxycarbonyl-L-lysine thiobenzylester esterase, a granule-associated biochemical marker, whereas IL-2 plus PMA was only marginally effective. Depletion of L3T4+ cells did not result in the abrogation of these effects. Lyt-2+ T cells that were incubated for 72 h with BSF-1 plus PMA accumulated N-benzyloxycarbonyl-L-lysine thiobenzylester esterase and secreted this intragranular marker after interaction with immobilized anti-T cell receptor mAb. These BSF-1/PMA-stimulated Lyt-2+, L3T4- T cells were also able to kill FcR positive target cells in a retargeting assay with a mAb to murine T3 Ag, providing evidence that BSF-1 plus PMA acted directly on precursors of cytotoxic T cells.

Organization of lymphocyte plasma membrane. Surface protein-membrane matrix interactions in B-cell lines of different stages of differentiation

Composition of surface proteins and their interactions with cytoskeleton or membrane matrix were compared in tumor B-cell lines of different stages of B-lymphocyte maturation. All studied B-cell lines were found to share a similar set of cell surface proteins, which are tightly associated with the cytoskeleton. The increase in amount of detergent-unextractable cell surface proteins with B-cell maturation suggested that differentiation of B lymphocytes was accompanied by development of specific interactions between surface proteins and elements of the cytoskeleton or membrane matrix. Using a recently developed procedure for lymphocyte plasma membrane fractionation we demonstrate changes in distribution of cell surface proteins in membrane matrix-rich and membrane matrix-poor plasma membrane fractions during B-lymphocyte maturation. Thus, cell surface proteins of the mature B-cell line MOPC-315 were predominantly found in the plasma membrane vesicles of a high buoyant density. These vesicles mostly contained plasma membrane proteins tightly associated with elements of the membrane matrix. In immature B cells (line 70Z3) virtually all surface proteins were detected in both low and high buoyant density membrane vesicles. The tendency to increased associations between surface proteins and cytoskeleton/membrane matrix with maturation of B cells could not be explained by increased amounts of filamentous actin, since no correlation was found between the amount of globular or filamentous actin and the degree of surface protein-cytoskeleton (membrane matrix) interactions.

Immunomodulating properties of a novel series of protein kinase C activators. The bryostatins

Low concentrations of the protein kinase C activators, bryostatins 1 and 2 synergized with recombinant B cell stimulatory factor-1 in triggering differentiation (granule enzyme expression) and cytotoxic T lymphocyte (CTL) development in naive, resting lymph node T cells. Bryostatin greatly enhances efficiency of recombinant interleukin-2 in triggering development of in vivo primed CTL during in vitro incubation, thereby providing experimental evidence for the efficacious use of lower concentrations of recombinant interleukin-2 for in vivo tumor rejection studies. Both bryostatins 1 and 2 were able to trigger cytotoxicity of CTL clones against antigen-nonbearing target cells and inhibited CTL cytotoxicity against Ag-specific target cells. Bryostatin 1 and 2 synergize with Ca2+ ionophores in triggering the exocytosis of cytolytic granules from CTL at very low concentrations. In view of the lack of tumor promoting activity of the bryostatins, the possible use of these agents in vivo is discussed.

Immunomodulating properties of a novel series of protein kinase C activators. The bryostatins

Low concentrations of the protein kinase C activators, bryostatins 1 and 2 synergized with recombinant B cell stimulatory factor-1 in triggering differentiation (granule enzyme expression) and cytotoxic T lymphocyte (CTL) development in naive, resting lymph node T cells. Bryostatin greatly enhances efficiency of recombinant interleukin-2 in triggering development of in vivo primed CTL during in vitro incubation, thereby providing experimental evidence for the efficacious use of lower concentrations of recombinant interleukin-2 for in vivo tumor rejection studies. Both bryostatins 1 and 2 were able to trigger cytotoxicity of CTL clones against antigen-nonbearing target cells and inhibited CTL cytotoxicity against Ag-specific target cells. Bryostatin 1 and 2 synergize with Ca2+ ionophores in triggering the exocytosis of cytolytic granules from CTL at very low concentrations. In view of the lack of tumor promoting activity of the bryostatins, the possible use of these agents in vivo is discussed.

Age-associated T-lymphocyte activation through mitogens in patients with multiple sclerosis and blood donors

In 128 patients with multiple sclerosis (MS) and 204 blood donors (control persons) the in vitro activation of 'Ficoll-purified' peripheral blood T lymphocytes was measured using the 3H-thymidine incorporation rate without (spontaneous proliferation) and with mitogen addition (concanavalin A, phytohemagglutinin). Mitogen responsiveness in control persons and MS patients decreased with age, reflecting a T-lymphocyte inherent mechanism for the diminution of responsiveness. The MS patients, ranging in age between 20 and 30 years, showed decreased mitogen responsiveness and a tendency to increased spontaneous proliferation compared to the control persons. These results could be an expression of a viral infection.

A novel cytotoxic T lymphocyte activation assay. Optimized conditions for antigen receptor triggered granule enzyme secretion

A method is described for the quantitative studies of cytotoxic T lymphocyte (CTL) activation. This functional assay is based on the measurements of secreted granule-associated enzymatic activity (BLT esterase (BLT-E) ) after incubation of CTL with activating stimuli. Immobilized mAb against CTL's antigen receptor (anti-TcR mAb), concanavalin A or a combination of PMA and ionophore A23187, were able to trigger the secretion of enzyme in the absence of target cells. Soluble anti-TcR mAb alone did not activate CTL, but using their conjugate with immobilized rabbit anti-mouse Ig antibody (RAMIg) TcR-mediated secretion of BLT-E was detected. Use of non-ionic detergents Nonidet P-40 or Triton X-100 (0.0125-0.2%) did not affect measurements of BLT-E activity. The efficiency of CTL exocytosis triggering by anti-TcR mAb which were immobilized on the surface of different plasticware is compared and conditions for studies of small and large numbers of CTL are described. The intensity of CTL response varies markedly with changes in buffer system, culture medium, additions of proteins. The optimal conditions for TcR complex triggered activation of murine CTL are described. Intensity of secretion can be easily manipulated by changing the surface density of immobilized anti-TcR mAb, thereby providing the possibility to screen inhibiting or activating agents (drugs or mAb) at selected sub-optimal levels of CTL activation. The potential for the use of described assay in screening of hybridoma supernatants for the presence of activating or inhibitory mAb against CTL's surface proteins is discussed. Since BLT-E secretion reflects exocytosis of granules from CTL, the conditions described here could be used for the detection of secretion of other markers of granules in future modifications of granule exocytosis assay.

Exocytosis of cytolytic granules may not be required for target cell lysis by cytotoxic T-lymphocytes

Secretory processes have been implicated in the mechanism of target-cell lysis by cytotoxic T-lymphocytes (CTL) (refs 1, 2). Both CTL and cytotoxic large granular lymphocytes have cytolytic granules, containing the cytolytic molecules 'perforin' and 'cytolysin'; perforin and cytotoxic lymphocytes can damage target cells through the membrane assembly of pores. The description of proteases which are cytotoxic cell-associated and granule-located has supported the granule exocytosis model of cytotoxicity mediated by cytotoxic lymphocytes, and has emphasized the similarities between cell-mediated and complement-mediated cytotoxicity. But recent experiments have challenged the importance of lytic granules and perforin in CTL activity. Here we report that CTL can be triggered to deliver a lethal hit to target cells even when exocytosis of lytic granules has been abolished by removal of extracellular calcium. This dissociation of exocytosis of granules and delivery of the lethal hit suggests that cytolytic granules may not be involved in target-cell lysis by CTL.

T cell antigen receptor triggered exocytosis in cytotoxic T lymphocytes is inhibited by soluble, but not immobilized monoclonal antibodies to Lyt-2 antigen

The effect of monoclonal antibodies (mAb) to surface antigens on the T cell antigen receptor (TcR)-triggered exocytosis of intracellular granules in cytotoxic T lymphocytes (CTL) was studied. Soluble anti-LFA-1, anti-TcR, and anti-Lyt-2 mAb inhibited both CTL-inflicted 51Cr-release from the target cell (TC) and TC-stimulated exocytosis of granules from cloned CTL. Soluble anti-TcR and anti-Lyt-2 mAb but not soluble anti-LFA-1 mAb inhibited exocytosis, which was triggered by solid-phase anti-TcR mAb. Immobilized anti-Lyt-2 did not inhibit secretion triggered by immobilized anti-TcR mAb; immobilized anti-LFA-1 mAb had an modest inhibiting effect. Inhibition of exocytosis by soluble anti-Lyt-2 mAb was greater when stimulating anti-TcR mAb were immobilized at a lower density on a plastic surface. When the requirement for TcR cross-linking was bypassed by synergistic action of phorbol ester and ionophore A23187, no inhibition of exocytosis by soluble anti-Lyt-2 mAb was detected. The obtained data point to steric hindrance as the most likely explanation of the inhibition of TcR-triggered CTL activation by anti-Lyt-2 mAb.

T cell antigen receptor triggered exocytosis in cytotoxic T lymphocytes is inhibited by soluble, but not immobilized monoclonal antibodies to Lyt-2 antigen

The effect of monoclonal antibodies (mAb) to surface antigens on the T cell antigen receptor (TcR)-triggered exocytosis of intracellular granules in cytotoxic T lymphocytes (CTL) was studied. Soluble anti-LFA-1, anti-TcR, and anti-Lyt-2 mAb inhibited both CTL-inflicted 51Cr-release from the target cell (TC) and TC-stimulated exocytosis of granules from cloned CTL. Soluble anti-TcR and anti-Lyt-2 mAb but not soluble anti-LFA-1 mAb inhibited exocytosis, which was triggered by solid-phase anti-TcR mAb. Immobilized anti-Lyt-2 did not inhibit secretion triggered by immobilized anti-TcR mAb; immobilized anti-LFA-1 mAb had an modest inhibiting effect. Inhibition of exocytosis by soluble anti-Lyt-2 mAb was greater when stimulating anti-TcR mAb were immobilized at a lower density on a plastic surface. When the requirement for TcR cross-linking was bypassed by synergistic action of phorbol ester and ionophore A23187, no inhibition of exocytosis by soluble anti-Lyt-2 mAb was detected. The obtained data point to steric hindrance as the most likely explanation of the inhibition of TcR-triggered CTL activation by anti-Lyt-2 mAb.

Antigen receptor-triggered secretion of a trypsin-type esterase from cytotoxic T lymphocytes

Exocytosis of cytolysin-containing granules from cytotoxic T lymphocytes (CTL) was studied with the use of granule enzyme (BLT esterase) as a convenient biochemical marker. Using cloned CTL, we demonstrate here that BLT esterase secretion into the supernatant is specifically triggered by antigen-bearing target cells and that this secretion is inhibited by soluble monoclonal antibodies against the antigen-specific T cell receptor (TcR). Immobilized anti-receptor antibodies induced efficient enzyme secretion in the absence of target cells, thus implying a direct involvement of TcR complex in triggering exocytosis of granules. These results support the role of the granule exocytosis in CTL functions and provide a quantitative and direct assay of a rapid CTL functional response to antigenic stimulation.

Antigen receptor-triggered secretion of a trypsin-type esterase from cytotoxic T lymphocytes

Exocytosis of cytolysin-containing granules from cytotoxic T lymphocytes (CTL) was studied with the use of granule enzyme (BLT esterase) as a convenient biochemical marker. Using cloned CTL, we demonstrate here that BLT esterase secretion into the supernatant is specifically triggered by antigen-bearing target cells and that this secretion is inhibited by soluble monoclonal antibodies against the antigen-specific T cell receptor (TcR). Immobilized anti-receptor antibodies induced efficient enzyme secretion in the absence of target cells, thus implying a direct involvement of TcR complex in triggering exocytosis of granules. These results support the role of the granule exocytosis in CTL functions and provide a quantitative and direct assay of a rapid CTL functional response to antigenic stimulation.

Clinical and biochemical aspects of the insulin autoimmune syndrome (IAIS)

A 44-year old patient presented with recurrent hypoglycemic attacks after ingestion of carbohydrates. High insulin levels in the range of 350 microU/ml (normal range less than 20 microU/ml) were detected which rose to peak levels of 2,460 microU/ml (normal range less than 300 microU/ml) after oral glucose. The apparently high insulin concentrations were caused by insulin autoantibodies interfering in the radioimmunoassay (RIA) system (and thus with correct insulin quantitation). 125I-insulin added to the patient's serum was not bound to dextran-coated charcoal but was precipitated with antihuman IgG serum. The antibodies bound human, porcine, and bovine insulin with similar affinity. Following Sephadex G-50 gel filtration, the patient's insulin eluted after the void volume. Free insulin was extracted from serum using Sep-Pak C 18 cartridges and characterized by high pressure liquid chromatography (HPLC); it eluted similarly to synthetic human insulin. Quantitation of free insulin during a hypoglycemic attack (3.5 h after oral glucose, with a blood sugar of 20 mg/dl) showed an increased insulin level of 50 microU/ml. Insulin receptor concentration on erythrocytes was near the lower normal limit. We believe that the insulin antibodies present in this patient's serum (who supposedly never received insulin) led to the formation of a large circulating insulin pool, binding the insulin released after glucose stimulation, and causing hypoglycemias by delayed postprandial liberation of bound insulin.