Evaluation of Cyclin D1 expression by western blotting methods and immunohistochemistry in breast cancer patients

PURPOSE

Considering that cyclin D1 had a prognostic and clinical value for breast cancer patients, adequate measurement of cyclin D1 is necessary.

METHODS

In this investigation, we detect cyclin D1 expression in tumour and peritumoral tissue of breast cancer patients by Western blotting method and by immunohistochemistry.

RESULTS

Cyclin D1 expression decreased significantly with each advanced clinical stage of disease and tumour size. Also, patients without lymph node involvement, with positive hormone receptors and Luminal A type of tumours had significantly increased the expression of cyclin D1. We show that cyclin D1 expression correlates with longer RFS in the entire group of patients, in the group of ER-positive and in the group of HER2-negative patients. Patients who were both ER and cyclin D1 positive had a better prognosis.

CONCLUSION

Taken together, our results, showing correlation of cyclin D1 with clinical stage, tumour size and lymph nodes, suggest that cyclin D1 expression, detected by Western blotting, could be considered as an additional marker for the staging of breast cancer, as well as a marker for longer RFS and survival in ER-positive breast cancer patients.

pSTAT3 expression associated with survival and mammographic density of breast cancer patients

BACKGROUND

Constitutive activation of STAT3 have been shown in several tumor types including breast cancer. We investigate STAT3 expresion as possible molecular marker for breast cancer early detection, as well as prognostic factor for determination of tumor agressiveness.

METHODS

In this study we measure p(Y705)STAT3 expression in tumor and adjacent tissue of breast cancer patients by Western blot. For relapse-free survival (RFS) and overall survival (OS) we used Log-Rank test.

RESULTS

We show that average expression of p (Y705) STAT3 in tumor tissue is higher compared to adjacent tissue. Moreover, we found that patients with HER2 positive receptors had significantly higher pSTAT3 expression compared to HER2 negative patients. We showed that patients with high mammographic density had significantly higher tumor expression of pSTAT3 compared to patients with low mammographic density. Also, we show that pSTAT3 expression correlates with longer RFS in the entire group of patients, as well as in the group of ER positive, in lymph node positive and in older group of breast cancer patients (with age over 50). Furthermore, in the entire group of patients, in ER positive, in lymph node positive and in older group of patient, high expression of pSTAT3 showed a better survival than low expression of pSTAT3.

CONCLUSION

Considering that the expression of pSTAT3 is associated with longer RFS and survival, it can be used as prognostic tools for determination of group of breast cancer patients with low-risk.

The Actual Role of LDH as Tumor Marker, Biochemical and Clinical Aspects

Lactate dehydrogenase (LDH) among many biochemical parameters represents a very valuable enzyme in patients with cancer with possibility for easy routine measurement in many clinical laboratories. Previous studies where mostly based on investigated LDH in serum of patients with cancer with aims to estimate their clinical significance. The new directions in investigation of LDH where based on the principle that tumor cells release intracellular enzymes trough damaged cell membrane, that is mostly consequence in intracellular mitochondrial machinery alteration, and apoptosis deregulation. This consideration can be used not only in-vitro assays, but also in respect to clinical characteristics of tumor patients. Based on new techniques of molecular biology it is shown that intracellular characteristics of LDH enzyme are very sensitive indicators of the cellular metabolic state, aerobic or anaerobic direction of glycolysis, activation status and malignant transformation. Using different molecular analyses it is very useful to analyzed intracellular LDH activity in different cell line and tumor tissues obtained from patients, not only to understanding complexity in cancer biochemistry but also in early clinical diagnosis. Based on understandings of the LDH altered metabolism, new therapy option is created with aims to blocking certain metabolic pathways and stop tumors growth.

HER2-positive breast cancer patients: correlation between mammographic and pathological findings

Human epidermal growth factor receptor 2 (HER2)-positive breast cancers represent a highly aggressive breast cancer subtype and are associated with a worse prognosis. This study was designed to investigate the mammography finding of HER2-positive breast cancer and to compare the results with the characteristics of HER2-negative breast cancer patients. From January 2010 to October 2011, mammography findings of 65 patients with pathologically confirmed HER2-positive breast cancers (n = 22) or HER2-negative breast cancers (n = 43) were retrospectively reviewed. The authors also reviewed pathological reports for information on the histological type and differentiation grade. Among the two types of breast cancer patients, estrogen receptor-negative/PR-negative/HER2-positive breast cancer patients most commonly had associated calcifications (18 of 22) on mammography. On mammography, cases with a cluster of calcifications usually were presented as pleomorphic calcifications (12 of 20) and branching calcifications (4 of 20). Patients with HER2-positive breast cancers showed a histological grade II. HER2-positive breast cancer patients usually had ductal invasive carcinoma (17 of 22). Moreover, postmenopausal patients showed a significantly higher frequency of HER2-positive tumours. Our results suggest that the imaging findings might be useful in diagnosing HER2-positive breast cancer patients.

Lactate dehydrogenase, catalase, and superoxide dismutase in tumor tissue of breast cancer patients in respect to mammographic findings

Lactate dehydrogenase (LDH), marker of anaerobic metabolism, is associated with highly invasive and metastatic breast cancer. Novel studies show that increased anaerobic metabolism (LDH), as well as activity of antioxidative enzymes (superoxide dismutase (SOD) and catalase (CAT)), is correlated with higher mammographic density, as known predictor of breast cancer risk. In this study, we measured LDH, MDH, and SOD activity in tumor and adjacent tissues of breast cancer patients by spectrophotometric assay. Mammograms were evaluated according to the American College of Radiology Breast Imaging Reporting and Data system. Mammographically dense breast tissue is associated with higher activity of LDH in tumor tissue of breast cancer patients. Moreover, patients with masses have significantly higher activity of LDH compared to patients with focal asymmetries or architectural distortion. Patients with spiculated mass margin had higher activity of LDH compared to patients with focal asymmetries or architectural distortion. Activity of LDH in patients significantly increases, while activity of CAT significantly decreases with the increase of BIRADS category. These results suggest that the association of activity of LDH and CAT in tumor tissue with mammographic characteristics could help in defining aggressive breast cancers.

In vitro increased natural killer cell activity of metastatic melanoma patients with interferon-α alone as opposed to its combination with 13-cis retinoic acid is associated with modulation of NKG2D and CD161 activating receptor expression

PURPOSE

Considering tumor-induced suppression of natural killer (NK) cell activity the aim of this study was to investigate the in vitro effect of a standard immunotherapeutic cytokine, interferon (IFN)α, and a less investigated agent, 13-cis retinoic acid (RA) on the functional and receptor characteristics of CD16-defined NK cells and their functionally diverse dim and bright subsets in patients with metastatic melanoma (MM).

METHODS

Peripheral blood lymphocytes (PBL) of patients with clinical stage IV MM were stimulated in vitro for 18 h in RPMI 1640 culture medium (CM) alone, CM supplemented with IFN-α (250 U7sol;ml), RA (10-6M) and their combination. NK cell activity was determined using standard 4 h radioactive cytotoxicity assay, while the expression of activating (NKG2D, CD1617rpar; and inhibitory (CD158a, CD158b) NK cell receptors on CD3-CD16+ NK cells and their functional bright and dim subsets were analyzed by flow cytometry.

RESULTS

NK cell cytotoxic activity was increased after in vitro treatment with IFN-α alone and in combination with RA, while only IFN-α induced increase in NKG2D and CD161 activating NK cell receptor expression. Contrary to this, RA treatment increased the expression of inhibitory KIR CD158b. IFN-α-obtained increase in CD161 expression was due to its induction on both NK cell subsets, while for NKG2D only on CD16bright subset.

CONCLUSION

The favorable enhancement of NK cell activity of MM patients obtained with IFN-α is associated with upregulation of activating NKG2D and CD161 receptors, while the lack of RA-associated upregulation is probably due to the shown increased expression of inhibitory KIR receptor CD158b after in vitro treatment with this agent.

Investigation of NK cell function and their modulation in different malignancies

NK cells have become a subject of investigation not only in the field of tumor immunology and infectious diseases, but also within all aspects of immunology, such as transplantation, autoimmunity, and hypersensitivity. Our early studies aside from investigating NK cell activity in experimental animals and humans included studies of perforin expression and modulation in this lymphocyte subset. As NK cell activity is modified by their environment, we showed clinical stage-dependent impairment of their activity and in vitro effect of different sera, Th1 cytokines, and their combination in breast cancer, Hodgkin's disease, and non-Hodgkin's lymphoma patients, especially with respect to metabolic and cell membrane changes of peripheral blood lymphocytes evaluated by spontaneous release of the enzyme lactate dehydrogenase (LDH) that led to the correction of the LDH enzyme release assay for natural cytotoxicity. By long-term immuno-monitoring of patients with malignancies, we also showed the kinetics of NK cell modulation during chemo-immunotherapy. In our more recent studies, we give data of NK function and novel families of NK cell receptor expression in healthy individuals that may be of help in NK cell profiling, by giving referent values of basic and cytokine-induced expression of some NK cell receptors either in evaluation of disease or in immuno-monitoring during cytokine therapy of patients with malignancies. Moreover, we give novel aspects of modulation of NK cell activity by cytokines approved for immunotherapy, IFN and IL-2, in melanoma and other malignancies with respect to alterations in new activating (NKG2D and CD161) and inhibitory (CD158a and CD158b) receptor characteristics and signaling molecules in CD16- and CD56-defined NK cells and their small immunoregulatory and large cytotoxic subsets in peripheral blood and lymph nodes, as NK cell-mediated killing of tumor cells depends on the balance between stimulatory and inhibitory signaling.

Association of decreased NK cell activity and IFNγ expression with pSTAT dysregulation in breast cancer patients

PURPOSE

Impaired IFNγ production in peripheral blood lymphocytes (PBL) and their subsets reflects immunosuppression and inadequate antitumor immune response in cancer patients. Decreased function of natural killer (NK) cells has not been investigated in breast cancer with respect to altered pSTAT signaling pathways.

METHODS

PBL of breast cancer patients and healthy controls were analyzed for IFNγ and pSTAT1 expression and NK cell activity using flow cytometry and (51)Cr-release assay, respectively. The level of pSTAT1, 3 and 5 was investigated by Western blotting.

RESULTS

Our results indicated that PBL and CD3(-) CD16(+) NK cells of patients had significantly lower level of IFNγ. The patients had a significantly decreased NK cell cytotoxicity compared to controls, with the decrease being dependent on the stage of disease. Positive correlation between IFNγ level in PBL and NK cytotoxicity in controls and patients was also shown. The PBL of patients, compared to controls, expressed lower level of pSTAT1, 3 and 5. The patients' T and NK cell subsets had lower pSTAT1 level.

CONCLUSION

This study indicates that pSTAT1 in PBL of breast cancer patients could be a biomarker of decreased NK cell cytotoxicity and IFNγlevel that are associated with progression of this disease.

TNF-α induced apoptosis is accompanied with rapid CD30 and slower CD45 shedding from K-562 cells

TNF-α can induce cell death (apoptosis and necrosis), and these effects mostly depend on expression of TNF-receptor superfamily molecules. As determination of certain intracellular enzymes like LDH, released from cultured tumor cells, reflects early membrane alterations, we compared LDH release with changes in cell surface membrane molecule expression during culture of K-562 cells in the presence of TNF-α. TNF-α-mediated CD45 and CD30 shedding is shown to be to be time- and dose-dependent and associated with significant increase in LDH release, with maximal effects after 24 h of treatment. The percentage of decrease of all examined cell surface molecules on K-562 cells after TNF-α treatment was not uniform and appeared to depend on the respective constitutive level of expression and molecule type. The presence of these molecules was confirmed in supernatants using Western blot analyses. These results indicated the complexity of events on the cell membrane, including early LDH release that is associated with a difference in shedding of CD30 and CD45. Shedding of CD30 occurs before apoptosis induction, while shedding of CD45 is associated with apoptosis.

An aggressive extramedullary cutaneous plasmacytoma associated with extreme alterations in the innate immune system

BACKGROUND

The role of natural killer (NK) cells in plasma cell diseases has not yet been fully characterized.

CASE REPORT

We present the case of a 47-year-old man with an extremely aggressive extramedullary plasmacytoma of the lung with associated cutaneous lesions, whose disease was accompanied by a significantly decreased number of NK cells (CD56+, CD16+, CD3-) in the peripheral blood, very low NK cell activity levels, and a decreased interleukin-2 production from cultured cells in vitro. Histology and immunohistochemistry of the lung and cutaneous lesions identified that the tumor was composed of clonal plasma cells which were CD38+++, CD138+++, lambda chain+, kappa chain-, and cytokeratin-. Bone marrow histology and cytology were initially normal. The disease progressed rapidly despite local radiotherapy and systemic chemotherapy, and the patient died shortly after diagnosis.

CONCLUSIONS

Cutaneous involvement in extramedullary plasmacytoma represents a clinically aggressive variant of plasma cell tumor, which runs a rapid course and has associated devastating effects on the patient's innate immune system.

Antiproliferative effect of 13-cis-retinoic acid is associated with granulocyte differentiation and decrease in cyclin B1 and Bcl-2 protein levels in G0/G1 arrested HL-60 cells

Retinoic acid (RA), similar to specific growth factors, can induce differentiation of proliferating promyelocytic precursors into terminally differentiated granulocytes, although little is known about effects of its 13-cis isomer on promyelocytic leukemia (PML). In this study we demonstrate that 13-cis-RA has a dose and time-dependent antiproliferative effect on HL-60 PML cell line, that it induces cell accumulation in resting G0/G1 phase of the cell cycle followed by an increase in CD11b granulocyte differentiation antigen expression. The obtained increase in the percentage of HL-60 cells in G0/G1 phase and complementary decrease in S phase of the cell cycle are accompanied by a decrease in the expression of cell cycle regulatory molecule cyclin B1. We also show the induction of interferon regulatory factor-1 (IRF-1) transcription that can, also, to some extent contribute to the antiproliferative effect of 13-cis-RA. Furthermore, down-regulation of Bcl-2 protein expression in 13-cis-RA treated HL-60 cells may contribute to sensitivity to apoptosis of growth arrested HL-60 promyelocytic cells.

Investigation of constitutive and cytokine-induced expression of pSTAT 1, 3, and 5 in PBL of breast cancer patients

3042

Background: Although cytokines mediate their effects by latent transcription factors, STATs, their dysregulation has not been much investigated in peripheral blood lymphocytes (PBL) of breast cancer patients. As alterations in the JAK-STAT pathway contribute to immunosuppression in cancer patients in this study, aside from baseline-level, we investigated the level and cytokine-mediated activation of STAT1, 3, and 5 in healthy controls and breast cancer patients. Methods: PBL (5x106/ml) of breast cancer patients in all four clinical stages, as well as healthy controls, were treated in vitro with culture medium (CM) alone, IFNα (250 IU/ml CM) and IL-2 (500 IU/ml) for 24h at 37°C. Induction of phosphorylated STAT proteins was assessed in cellular lysates by Western blotting using monoclonal anti-STAT1, 3, and 5 antibodies. Treated PBL were also analyzed for IFNγ using an intracellular flow cytometry assay. Results: Our results indicate that untreated PBL of breast cancer patients, compared to healthy controls, express a significantly lower baseline level of pSTAT1, 3, and 5. The induction of pSTAT1 expression by IFNα, similar to the induction of pSTAT3 and pSTAT5 by IL-2, is significant for healthy controls and breast cancer patients, although the effect in patients is significantly below that for healthy controls. Moreover, the induction of pSTAT5 by IL-2 is of a higher magnitude than pSTAT3. PBL of breast cancer patients, compared to healthy controls, have a lower level of IFNγ. The production of IFNγ in PBL is enhanced by IFNα, as well as IL-2, although in breast cancer patients to a much lower level than in healthy controls. Conclusions: These results provide evidence that evaluation of STAT expression in PBL of breast cancer patients could be of diagnostic and therapeutic significance for cytokine-based therapy.

No significant financial relationships to disclose.

Clinical stage-depending decrease of NK cell activity in multiple myeloma patients

Natural killer cells, as an important subpopulation of cells of the innate immune system have an essential role in defense of the rise and spread of malignancy. These cells have a CD3-CD16 + CD56+ phenotype and they are functionally defined by their ability to lyses tumor cells. We here show that decrease of NK cell activity was significantly associated with advanced clinical stage, increased lactate dehydrogenase (LDH), percentage infiltration of bone marrow with plasma cells, and beta-2 microglobulin. The patients with higher NK cell activity at presentation after receiving VAD protocol have better cumulative survival in comparison with those with low NK cell activity.

Monitoring of NK cell activity and serum LDH in metastatic melanoma patients treated with DTIC and interferon-alpha2a, with or without retinoic acid

19000

Background: The activity of NK cells, expression of CD69, and serum LDH were evaluated in terms of response to therapy in metastatic melanoma patients. Methods: In phase II clinical study metastatic melanoma (MM) patients were treated with DTIC (800 mg/m2, d1) and IFN-alpha 2a (5×106 IU/m2 s.c., d2–6 (group A, n=25) and 28 patients received the same therapy supplemented with RA, 60 mg/d, d1–10 (group B). Before and after each therapy cycle NK cell activity, CD69+NKcells and LDH were monitored in patients and 39 healthy controls. Results: There is no significant difference in OR (group A 32%, B 21%), in time to progression between groups. NK cell activity was significantly decreased pretherapy in both groups, with a significant increase in the 1st cycle in both groups. NK cell activity did not show significant correlation with OS in group A compared to group B (p=0.445). 20% of patients in group A with pretherapy NK cell cytotoxicity above 30% had better survival from month 3 to 12 of follow-up and a longer maximal survival (1.2 vs. 1.0 year, respectively). In comparison to pre-therapy values, all responding MM patients had a significantly higher increase of CD69 expression on CD56+ NK cells, while the increase was only significantly higher in responders in group B. Analyses of serum LDH level show a significantly higher time and therapy cycle-dependent decrease in group A compared to group B (50% vs. 25%, respectively). However, it is shown that responders in group B had a significantly greater decrease in serum LDH level compared to responders in group B (70% vs. 20%, respectively), if the level after a cycle was evaluated in terms of pretherapy values, as well as a greater decrease if the evaluation in each cycle was done compared to each pretherapy value (35% vs. 20%, respectively). Conclusions: Even though there is no significance in clinical response between patients in group A and B, in agreement with a steady-state pattern of NK cell activity, the fact that only responders in group B had a significant increase in CD69 expression on CD56+ NK cells, as well as the finding that the decrease in serum LDH was significantly greater in patients in group B, implicates favorable imunopotentiating and antitumor effect of RA in the therapy of metastatic melanoma.

No significant financial relationships to disclose.

Pretherapy predictive immunomodulation of NK cell activity and expression of activating and inhibitory receptors in stage IV melanoma patients

12514

Background: As melanoma (MM) is an immunogenic tumor with poor response to chemotherapy immunomodulating agents are applied in order to potentiate cytotoxic effect of chemotherapy and enhance antitumor immune response. Beside therapeutic benefit of IFN-α and IL-2, 13-cis retinoic acid (RA), as an antiproliferative, differentiating and immunomodulating agent is also investigated. The effect of these agents on NK cells, as main innate immune system effectors, is being investigated. Methods: 35 patients with MM in stage IV prior to therapy and 20 controls were investigated. We evaluated NK activity and the expression of activating (NKG2D and CD161) and inhibitory (CD158a and CD158b) receptors on freshly isolated PBL. Predicitive immunomodulation was performed in 18 h in vitro treated PBL with rh IL-2 (200U/ml), IFN (250U/ml), RA (10−6M), and their combination. Results: Native NK cell cytotoxic activity and expression of NKG2D and CD161 activating receptors on fresh NK cells in MM patients is significantly decreased compared to controls. Predictive treatments with IL-2, IFN, IFN and RA, unlike RA alone, gave a significant increase in NK cell activity of MM patients. Singly, IFN also induced a significant increase in CD161 expression on NK cells in patients. The treatments gave no change in the expression of CD158b, while RA, alone, induced significant decrease in the expression of the inhibitory CD158a antigen. Evaluation of mRNA of transcription molecule IRF-1 shows that it is promptly up-regulated by IFNα, more by IFNα and RA, while single RA has no effect on mRNA induction. Conclusions: Considering that the mechanism of applied immunomodulating agents is continually investigated in order to optimize the dose and schedule of their administration and, also, considering controversial clinical results of RA application, alone, or with IFN, in this study we give novel results that show no significant effect of RA, whereas, IFN-induced increase in NK cell activity of MM patients is for the first time associated with the increase in the expression of NKG2D and CD161 receptors on CD16+NK cells, and not with the decrease in some inhibitory receptors, as the activity of NK cells is regulated by the balance of these two types of signals.

No significant financial relationships to disclose.

TNF-alpha induced changes in cell membrane antigen expression on K-562 cells associated with increased lactate dehydrogenase (LDH) release

TNF-alpha is a pleiotropic cytokine, which induces death of sensitive cells, whose effect depend on cell membrane receptor expression, cell cycle phases, as well as on intracellular ratio of pro- apoptotic and anti-apoptotic molecule expression. Since determination of LDH release from cultured cells in vitro, reflects early membrane alterations, we estimated and compared LDH release from cultured cells with changes in cell membrane antigen expression on K-562 cells after TNF-alpha treatment by flow cytometry. The significant increase in LDH release activity and cytotoxicity values was associated with decrease in membrane molecule expression for CD45 and CD30 as well as for low expressed CD45RA and CD38 after TNF-alpha treatment. However, percentage of decrease of all examined molecules is not uniform, and appears to depend on the respective level of pre treatment values expression and molecule type. These results indicated the complexity of events on cell membrane, including association between increasing LDH release and decrease of antigen expression of membrane molecules following TNF-alpha mediated processes.

TNF-? induces changes in LDH isotype profile following triggering of apoptosis in PBL of non-Hodgkin?s lymphomas

Based on the possibility of tumor necrosis factor (TNF)-alpha to perform multiple and opposite biologic effects, we simultaneously investigated in vitro its effects on intracellular lactate dehydrogenase (LDH)-H and LDH-M isoenzyme activity and morphological characteristics following induction of apoptosis in peripheral blood mononuclear cells (PBMC) of non-Hodgkin's lymphoma patients (NHL) prior to and after the end of applied chemotherapy. TNF-alpha showed a significant increase ( p<0.05) of LDH-H and LDH-M activity in sonified PBMC of healthy controls after 18 h cultures accompanied with an increase of apoptotic index (AI) from 2.3 to 16.2%. Contrary to this, in PBMC of NHL patients prior to therapy TNF-alpha induced a significant decrease ( p<0.05) of LDH-H isotype activity. In patients after administration of chemotherapy, TNF-alpha in a dose of 100 U/ml induced a significant increase ( p<0.05) of LDH-M isotype activity, but not of LDH-H. In the PBMC of NHL patients prior to chemotherapy, TNF-alpha in vitro induced an increase of AI from 2.8 up to 6.8%, while in PBMC of NHL patients after applied chemotherapy AI changed from 7.2 to 14.4%. However, there was no significant difference in the increase of apoptosis in PBMC of NHL patients with high-grade malignancy and high rate response among patients who received first-line therapy, high-dose therapy, or third-line therapy regimens after in vitro TNF-alpha treatment. These results indicated different susceptibilities of PBMC of NHL to TNF-alpha when effects were analyzed by determination of intracellular LDH isotype profile and induction of apoptosis prior to and after administration of therapy in comparison to effects on healthy controls PBMC.

Analysis of perforin expression in human peripheral blood lymphocytes, CD56+ natural killer cell subsets and its induction by interleukin-2

In this study new evidence is obtained by the use of an anti human perforin monoclonal antibody (mAb), anti P1, concerning the number of perforin positive cells in human peripheral blood lymphocytes (PBL). It is shown that about 23% of PBL is perforin positive and that this percent increases by the treatment in RPMI 1640 medium alone to 33% and with 1000 U r hIL-2 to 46%. Assessment of the cytotoxicity potential of NK cells from PBL, freshly isolated and treated, against tumor cell line K562 by the standard NK cell 4-hr 51-chromium release assay, indicates a significant enhancement in their cytotoxicity. By FACStar sorting and analysis of the CD56+ NK cell population new evidence is obtained which shows that about 25-30% of this population represents the CD56bright+ subset, while 70-75% represents the CD56dim+ subset. As the two subsets were shown to differ functionally they were stained with anti P1 for the evaluation of perforin content and it was found that both of them are positive for perforin from 97-99%, suggesting that the functional difference is not due to perforin content. In this sense, as NK cells are constitutively positive for perforin, the increase in the cytotoxicity of NK cells induced by IL-2 is most likely due to the synthesis and expression of various adhesion molecules on NK cells which increase their cytotoxic potential, as well as, that the detected increase in the number of perforin positive cells by this lymphokine does not belong to NK, but to the T lymphocyte population. The data obtained in this study indicate the possibility of perforin detection in human lymphocytes by an anti human perforin mAb and the change in the number of perforin positive cells after stimulation with interleukin-2.