[Epidural abscess secondary to the implantation of a thoracic catheter]

Spinal compression related to the formation of an epidural abscess after epidural blockade is a rare but serious complication. We report the case of a male patient in whom a thoracic epidural catheter was implanted to provide analgesia after trauma involving fracture ribs. The patient developed an epidural abscess within one week of implantation. Delay in diagnosis led to persistent neurogenic bladder symptoms in spite of aggressive treatment. We review causal factors, mechanisms of formation, pathogenesis, diagnosis and management, as well as possible relation between injury and abscess formation. We also emphasize the importance of adequate vigilance as well as rapid diagnosis and adoption of therapeutic measures in order to avoid permanent sequelae such as paresis, sensory deficits or mechanical sphincter dysfunction.

Long-term treatment with recombinant interferon alpha-2b prolongs survival of asymptomatic HIV-infected individuals

RATIONALE AND OBJECTIVE

Early long-term treatment with recombinant interferon (IFN) alpha-2b delayed disease progression in asymptomatic Human Immunodeficiency Virus (HIV) carriers in a randomized trial that lasted from October 1987 to February 1992 (14). The aim of the work reported in this paper was to observe if there was also an effect on survival when the same patients were followed-up further.

DESIGN AND INTERVENTIONS

IFN alpha-2b was given 3 x 10(6) IU, 3 times weekly. The control group did not receive any treatment. The main end-point for this evaluation was death due to any cause. The deadline was August 1995.

POPULATION

Subjects were anti-HIV-1 seropositive, Western blot-confirmed, asymptomatic (CDC group II), or with generalized lymphadenopathies (CDC group III). The groups had 79 (control) and 83 (IFN) patients.

MAIN RESULTS

Mean survival was longer in the IFN group (95% CI: 127-152 vs. 101-120 months since infection or 80-90 vs. 70-82 months since the start of treatment). Survival rates were higher in IFN-treated individuals (61-77% vs. 24-54% at 10 years of infection or 53-69% vs. 34-52% at 7 years of treatment or follow-up). It was also confirmed that disease progression is significantly slower in IFN-treated patients. There were 23.4 vs. 3.2% long-term survivors in the IFN and control groups, respectively (p = 0.005). IFN-treated patients had fewer AIDS-related malignancies (5 vs. 11), mainly Kaposi's sarcomas (1 vs. 5). This difference was not statistically significant, but clinically interesting. There was no difference in survival if measured since the onset of AIDS.

CONCLUSION

IFN alpha treatment given from the early stages of infection, but not after the appearance of AIDS symptoms, can prolong survival.

Adverse clinical outcome in Hodgkin's disease is associated with loss of retinoblastoma protein expression, high Ki67 proliferation index, and absence of Epstein-Barr virus-latent membrane protein 1 expression

Previous studies have shown that in non-Hodgkin's lymphomas and others neoplasms, tumoral progression, treatment response, and outcome are related to the expression of different oncogenic and tumor suppressor proteins. This study aimed to determine the prognostic significance of the expression of p53, bcl2, retinoblastoma protein (Rb), Ki67, CD15, and latent membrane protein 1-Epstein-Barr Virus (LMP1-EBV) proteins in Hodgkin's disease. A retrospective study was performed on 140 patients collected at the 11 participating centers belonging to the Spanish Collaborative Group for the Study of Hodgkin's Disease. A highly sensitive immunohistochemical method with previous microwave-induced antigen retrieval technique was used for the demonstration of the above-mentioned proteins. A Cox's multivariate analysis was performed to evaluate the impact of the variables in the overall survival, together with a logistic regression model for the achievement of complete remission. Univariate statistical analysis confirmed the prognostic significance of the alredy known clinical parameters: stage, age over 60 years, and B symptoms. High proliferation index (Ki67) and loss of Rb expression were also found to be adverse prognostic factors influencing respectively lower overall survival and failure to achieve complete remission. Multivariate analysis confirmed the independent significance of these two parameters and additionally identifies LMP1-EBV expression as a favorable prognostic marker, in relation with overall survival. Histopathological type, p53, bcl2, and CD15 expression lack significant influence on the outcome of this series. The progression of the disease or the response to treatment in HD patients is the consequence of the interrelationship of different factors, among which LMP1 expression, loss of Rb, and high growth fraction seems to play a more relevant role.

Cellular and subcellular distribution of 7B2 in porcine Merkel cells

BACKGROUND

Merkel cells are neuroendocrine cells located in the skin and oral mucosa of various mammalian species. These cells express multiple peptides as well as serotonin. Although the precise function of Merkel cells is still unknown, different studies support its role as mechano-electric transducer. 7B2 granin (secretogranin V) is a polypeptide isolated from the pituitary gland and present in the dense-cored granules of neuronal and paraneuronal cells.

METHODS

The expression of the 7B2 in Merkel cells of pig snout skin was analysed by immunohistochemical techniques. The streptavidin-biotin peroxidase complex procedure was employed for light microscopy. A postembedding method using immunoglobulin-colloidal gold complexes was employed for the ultrastructural studies.

RESULTS

Immunoreactivity for 7B2 was observed in virtually all Merkel cells, both in epidermis and vibrissae. The immunostaining was shown in the basal side of cytoplasms where neuroendocrine granules were accumulated. Immunoelectron microscopy allowed us to demonstrate that 7B2 labelling was located on the electrondense granules. Nuclei and epidermal nerve terminals associated with merkel cells did not show immunoreactivity.

CONCLUSIONS

The polypeptide 7B2 is present in the dense-cored granules of Merkel cells. This result is consistent with the possible role for 7B2 in secretory granules' processing. To our knowledge this is the first evidence of 7B2 protein in Merkel cells.

Cellular distribution of prolactin receptors in human digestive tissues

In the present study we analyzed the expression of prolactin receptors (PRLR) in human digestive tissues by immunohistochemistry. PRLR immunoreactivity was primarily localized in the cytoplasm. However, in some organs (liver and salivary glands) a nuclear positivity was also found. The liver was used as control and showed a diffuse immunostaining in the parenchymal cells. In the gastrointestinal tract, PRLR immunoreactivity was observed in the mucosa, muscularis layer, and nervous plexuses. The more intense immunostaining in the mucosa of the different segments was as follows: esophagus, superficial layers of the stratified squamous epithelium and mucous glands; stomach, parietal cells; small intestine, absorptive and Paneth cells; and colon, surface epithelium and superficial half of the crypts of Lieberkühn. In the salivary glands, immunoreactivity was strong in the mucous tubules, moderate in the ducts, and weak in the serous cells. Endocrine pancreas showed a more intense immunoreactivity than the pancreatic acini. By serial sections of the islets of Langerhans we showed that immunostaining was confined to B cells. These findings demonstrate the widespread distribution of PRLR in human digestive tissues and its localization both in cytoplasms and nuclei.

Mucosal mantle cell (centrocytic) lymphomas

The morphology, phenotype, genotype and clinical behaviour of four cases of mantle cell lymphoma (centrocytic lymphoma) presenting primarily in mucosa (two gastric, one in large bowel and one tonsillar) are reviewed. Their relationship with the broader group of mantle cell and mucosa-associated lymphoid tissue (MALT) lymphomas is also discussed. All four tumours showed a monomorphic picture of mantle cells (centrocytes) arranged in a diffuse, or vaguely nodular, pattern. Scattered non-neoplastic germinal centres were entrapped within the tumour cells, although there was no follicular colonization. In two cases distinct epithelial infiltration by tumour cells was observed. All four tumours had a CD19, CD20, CD5, IgD, Leu8 immunophenotype, whereas KiM1P and CD10 expression were absent. DRC antibody showed loose aggregates of dendritic cells in three of four cases. Three cases showed PRAD-1/Cyclin D1 overexpression by Northern blot analysis. Although we were not able to detect bcl-1 rearrangement in the major translocation cluster (MTC) breakpoint, the possibility of bcl-1 rearrangement involving other cluster breakpoints cannot be ruled out. The four cases evolved as a disseminated disease, involving either peripheral lymph nodes, spleen or bone marrow. The biological behaviour of mantle cell lymphoma presenting in mucosa appears, irrespective of localization or macroscopic presentation, similar to that of nodal mantle cell lymphoma. Their tendency to dissemination contrasts with MALT lymphomas, which tend to remain localized, and from which mucosa mantle cell lymphoma must be distinguished. The presence of lymphoepithelial lesions does not seem to be a useful differential feature, since occasional epithelial infiltration was seen in two cases. Reactivity with CD5 appears to be especially useful in distinguishing these, since all four cases were clearly positive, in contrast with what is usually found in MALT lymphomas.

Neural cell adhesion molecule immunoreactivity in Merkel cells and Merkel cell tumours

We have analysed the expression of the neural cell adhesion molecule (NCAM) in normal Merkel cells of pig and human skin, and in nine neuroendocrine carcinomas of the skin (Merkel cell carcinomas). NCAM immunoreactivity was observed in virtually all Merkel cells, both in epidermis and vibrissae of pig snout skin and in human epidermis. Immunostaining surrounded the entire surface of Merkel cells and was not restricted to the contact areas between Merkel cells and nerve terminals. All Merkel cell carcinomas studied were also positive for NCAM. The immunostaining pattern of the tumour cells was similar to that observed in normal Merkel cells; the immunoreactivity was confined to the cell membranes. These results suggest that NCAM may be used as an immunohistochemical marker for both Merkel cells and Merkel cell tumours.

Bone marrow involvement in anaplastic large cell lymphoma. Immunohistochemical detection of minimal disease and its prognostic significance

Bone marrow involvement by anaplastic large cell anaplastic large cell (ALC) lymphoma can be difficult to detect on routine morphologic examination alone. In a series of 42 patients with ALC lymphoma, the authors analyzed: (1) the usefulness of a limited panel of monoclonal antibodies directed against CD30 (Ber-H2, HRS4) and epithelial marrow involvement on routinely processed biopsy specimens; and (2) the prognostic significance of bone marrow involvement as detected on both morphologic and immunohistochemical grounds. On conventional examination, 17% of the patients were found to have bone marrow involvement at diagnosis. However, after immunohistochemical analysis, occult malignant cells were detected in 23% of the patients with negative bone marrow biopsy on routine histology. The low percentage of positive cases on routine morphologic examination compared to immunohistochemical examination was related to: (1) the scarcity of neoplastic cells which were scattered among hematopoietic cells; (2) the difficulty of distinguishing malignant cells from immature hematopoietic elements; and (3) the absence of alteration of the reticulin network. The authors observed a significant association between marrow infiltration and the presence of hematologic abnormalities (mostly anemia or cytopenias) at diagnosis, both in children and adult patients. More importantly, a significant lower survival was seen in patients with bone marrow involvement compared to those without bone marrow involvement. Immunohistochemistry with anti-CD30 and anti-EMA antibodies should be performed systematically in bone marrow biopsies from patients with ALC lymphoma to reliably identify the presence of bone marrow involvement that appears to carry a poor prognosis.

Monocytoid B cells. A comparative clinical pathological study of their distribution in different types of low-grade lymphomas

Neoplastic monocytoid B-cells (MBCs) are present in different amounts in several types of non-Hodgkin's lymphomas (NHLs), including monocytoid B-cell lymphoma (MBCL), splenic marginal zone lymphoma (SMZL), mucosa-associated lymphoid tissue (MALT) low-grade B-cell lymphomas, and follicular centroblastic-centrocytic (CB-CC) lymphomas. In an attempt to clarify the relationships between different groups of tumors with a significant monocytoid component, we studied six primary lymph node MBCL, three SMZL, seven MALT lymphomas, and four CB-CC with monocytoid differentiation. Their clinical, morphological, immunohistochemical and molecular features were compared. The results show wide overlapping between MALT and MBCL in terms of morphology, immunophenotype, and molecular features. Follicular colonization was a characteristic finding in both groups. Some MBCL revealed mucosal involvement during the course of the disease, suggesting a possible MALT origin. Our data support the suggestion that the use of the term MBCL should be discontinued in cases with mucosal involvement, as they are probably examples of lymph node involvement brought about by MALT lymphomas. Although SMZL have some overlapping features with MBCL and MALT lymphomas, some of the clinical and morphological specific findings justify their distinction from the other groups. The CB-CCs with monocytoid differentiation frequently harbored t(14;18), lacking any significant differentiating features from conventional follicular CB-CC lymphomas. Additional studies are needed to define the molecular features of MBCL and other marginal zone tumors.

Use of recombinant interferon-alpha in human immunodeficiency virus (HIV)-infected individuals

RATIONALE AND OBJECTIVE

Interferon alpha (IFN-alpha) has anti-retroviral activity and is a possible HIV infection-limiting factor. The aim of this work is to prevent or delay disease progression in asymptomatic Human Immunodeficiency Virus (HIV) carriers.

DESIGN AND INTERVENTIONS

Recombinant IFN alpha-2b (3 x 10(6) IU 3 times weekly) was compared to no treatment (control) in a randomized trial. Endpoints were: (i) appearance of any CDC group IV symptoms and (ii) disease progression (which excluded shifts to group IVC2 or reversible IVA, or IVB). The trial lasted from October 1987 to February 1992.

SETTING

The trial was performed at the "Santiago de las Vegas" sanatorium, a specialized institution for the care of HIV-infected and AIDS patients.

POPULATION

Subjects were anti-HIV-1 seropositive, Western blot-confirmed, asymptomatic (CDC group II), or with generalized lymphadenopathies (CDC group III). The groups had 79 (control) and 71 (IFN) patients.

MAIN RESULTS

Long-term IFN-alpha treatments significantly reduced the proportion of patients who shifted to any group IV (control: 46/79; IFN: 14/71; p < 0.001) or developed AIDS (control: 27/79; IFN: 12/71; p < 0.05). IFN also delayed progression to AIDS (95% confidence interval for 0.5 probability of progression) from 67-83 to 116-180 months after infection. The IFN group had significantly less opportunistic infections and non-infectious complications. CD4 cell count and hemoglobin decreased in the control but not in the IFN group. Fewer IFN-treated patients developed positive serum HIV antigen detection.

CONCLUSION

IFN alpha treatment during the early stages of infection seems to be beneficial to the patients.

Immunohistochemical location of prothymosin alpha in regenerating human hepatocytes and hepatocellular carcinomas

In the present paper we analysed the presence of prothymosin alpha (ProT) in human liver. In normal liver, ProT immunostaining was found in the nuclei of bile duct cells, but not in the hepatocytes. In contrast an intense immunoreactivity was observed in regenerative hepatocytes of chronic hepatitis, cirrhosis and in hepatocellular carcinomas. In all cases the immunostaining was restricted to the nuclei, but the nucleoli were always negative. Similar results were obtained for proliferating cell nuclear antigen. These findings confirm that ProT is related to cell proliferation and provides a new immunohistochemical proliferation marker for routinely processed samples.

A comparative immunohistochemical study of phaeochromocytomas and paragangliomas

There is no definite morphological distinction between phaeochromocytomas and paragangliomas. We, therefore, attempted to determine the universality and differential utility of a panel of tumour markers for diagnosis in formalin-fixed, paraffin-embedded specimens. Antibodies to neuron-specific enolase (NSE), chromogranin, synaptophysin, Leu-7, neurofilaments, cytokeratins, carcinoembryonic antigen (CEA), melanoma antigen HMB-45, S-100 protein and glial fibrillary acid protein (GFAP), were used on 11 phaeochromocytomas and 8 paragangliomas. NSE reactivity was detected in 10 phaeochromocytomas and in all paragangliomas. Chromogranin reactivity was found in all but two cases (one phaeochromocytoma and one paraganglioma). Synaptophysin reactivity was present in 10 phaeochromocytomas and in the 8 paragangliomas. Ten phaeochromocytomas stained for Leu-7, but none of the paragangliomas did. S-100-positive cells (sustentacular or type II cells) were found in 8 phaeochromocytomas and 7 paragangliomas. GFAP stained sustentacular cells of only one paraganglioma. Only in 5 phaeochromocytomas was there a focal reaction by neurofilaments. Cytokeratins, CEA and HMB-45 were never detected. We conclude that NSE, chromogranin, synaptophysin and S-100 protein are useful markers of both types of tumour, whereas GFAP staining is limited to a small number of these neoplasms. Leu-7 reactivity seems to favour diagnosis of phaeochromocytoma rather than paraganglioma, but further studies with larger series are needed to confirm this. Unlike previous reports, we did not find cytokeratin or HMB-45 immunostaining in any case.

Evolution of prothymosin alpha and proliferating cell nuclear antigen (PCNA) immunoreactivity through the development of rat ovarian follicles

The cellular distribution of prothymosin alpha (ProT) was studied in ovarian follicles of adult cycling rats. We found positive granulosa and theca cells throughout follicular maturation. When both ProT and proliferating cell nuclear antigen (PCNA) immunoreactivity was studied, we observed that both proteins were expressed in the same granulosa and theca cells, although sometimes ProT immunoreactivity was weak or absent in the mitotic (M) phase. Moreover, both peptides share the nuclear distribution, but ProT immunoreactivity was never seen in nucleoli. Therefore, we conclude that in mitotic cells ProT is expressed only in actively proliferating cells, since all ProT-positive cells were also positive for PCNA. ProT and PCNA immunoreactivities during the meiotic division were studied in oocytes. The presence of PCNA was, unlike ProT, constant throughout follicle development (except atretic oocytes). Oocytes expressed ProT from primordial follicles to the eighth generation, but more developed oocytes and atretic oocytes were not immunoreactive. In hypophysectomized rats, all oocytes were immunoreactive. Interestingly, in hypophysectomized rats treated with follicle stimulating hormone (FSH) that promoted follicle development, the more developed oocytes did not show ProT immunoreactivity. Since hypophysectomized rats were not treated with luteinizing hormone we conclude that ProT expression is not required to complete meiotic division I.

Tissue concentrations of prothymosin alpha: a novel proliferation index of primary breast cancer

In 71 patients with classic invasive ductal carcinomas, levels of prothymosin alpha (PT alpha), as assayed by a radioimmunoassay that detects thymosin alpha 1 (the NH2-terminal fragment of PT alpha), were significantly greater in tumour samples than in normal breast tissue. PT alpha levels were correlated with (a) the number of positive axillary lymph nodes (rs = 0.5384, P < 0.01), and (b) the percentage of tumour cells in the S or G2/M phase as assessed by flow cytometry (rs = 0.5027, P < 0.01). Since the beginning of this study in 1989, 21 patients have presented distant metastases, all of whom were previously shown to have tumour PT alpha levels greater than 124 ng of thymosin alpha 1/mg protein. The present report indicates that PT alpha might be used to identify breast cancer patients at high risk for distant metastases.

Prothymosin alpha expression in lymph nodes and tonsils: an optical and ultrastructural study

Prothymosin alpha (ProT alpha) distribution in human and rat lymph nodes and human tonsils was studied by means of immunohistochemical methods, using specific antibodies raised against thymosin alpha 1. We observed ProT alpha immunoreactivity in lymphoid cells of the germinal centers both in humans and rats. In human tonsils, positive cells were also seen in the basal layer of the surface epithelium. These results support the hypothesis that ProT alpha expression is restricted to actively proliferating cells. Immunoelectron microscopy revealed that ProT alpha was located in the nucleus, mainly in the border between euchromatin and heterochromatin.

[Alagille's syndrome: a family case and its association with hepatocellular carcinoma]

Two cases of Alagille syndrome are reported, father and son. This, a 6-year-old boy, presented with neonatal cholestasis but thereafter evolved with progressively decreasing jaundice and persisting pruritus. A liver biopsy confirmed the absence of intrahepatic bile ducts with preservation of hepatic architecture and no fibrosis. The patient had a characteristic phenotype: short stature, triangular face, deep eyes with hypertelorism, partial embryotoxon and data of peripheral pulmonary artery stenosis. His father died 43-year-old by a hepatocarcinoma. His liver biopsy showed also absence of intrahepatic bile ducts. In addition to the association Alagille's syndrome hepatocarcinoma (previously reported in six cases, three into the same family), it should be stressed in this case the long survival and the fact he had many children: the case with Alagille's syndrome, five children in good health, and one who died shortly after birth.

Immunohistochemical demonstration of neuronal and astrocytic markers and oncofoetal antigens in retinoblastomas

General opinion is that retinoblastomas, though not everyone agrees with that view. Some authors suggest that retinoblastomas are derived from a primitive retinal cell able to differentiate into both neuronal and glial cell lines. The aim of the present work was to study immunohistochemically the expression of neuronal and astrocytic markers in retinoblastomas and at the same time the presence of the oncofoetal antigens carcinoembryonic antigen (CEA) and alpha Foeto Protein (AFP), since patients with retinoblastomas often show high oncofoetal antigen in serum levels. For this purpose we employed the streptavidin-biotin immunoperoxidase technique in 13 cases of retinoblastoma to evaluate the presence and distribution of neuron-specific enolase (NSE), neurofilament protein (NF), glial fibrillary acidic protein (GFAP), S-100 protein, CEA and AFP. All 13 tumours studied stained for NSE. Seven of them showed GFAP- and S-100 positive perivascular glial cells as well as cells distributed randomly in the tumour that were interpreted as non tumour cells. All 13 retinoblastomas lacked detectable NF, CEA, and AFP. These results support the idea that retinoblastomas are neuronal tumours, although retinal glial cells may become incorporated in the tumour and proliferate in response to the tumour.

An analysis of the relationship between the cellular distribution and the rate of turnover for the separate classes of unoccupied, noncovalently occupied, and covalently occupied insulin receptor

To further investigate insulin's role in regulating the turnover of insulin receptor during down-regulation in 3T3-L1 adipocytes, the relationship between the cellular distribution and turnover of unoccupied, noncovalently occupied, and covalently occupied receptor was examined. At steady-state 12% of the unoccupied receptors and 46% of covalently occupied receptors are intracellular. The apparent first-order rate constant (Kapp) for turnover of the total pool of covalently occupied receptors (0.16 h-1) is 3.8-fold higher than that for unoccupied receptors (0.042 h-1). When unlabeled insulin is added, identical values for both Kapp (0.10 h-1) and distribution (26% internal) are measured for noncovalently and covalently occupied receptors. The rate constant (Kdeg), describing the relative sensitivity of internalized receptor to degradation, is identical (0.36-0.41 h-1) for unoccupied, noncovalently occupied, and permanently occupied pools of internal receptor. Mechanisms for down-regulation postulating: (a) an occupancy-dependent alteration in the conformation of internal receptor increasing receptor sensitivity to internal proteases, (b) a preferential sorting of internal occupied receptor to degradative pathways, or (c) induction of intracellular proteases by insulin, would all reflect a substantial change in Kdeg for occupied receptor and thus are unlikely mechanisms by which insulin increases the rate of receptor turnover. The turnover of insulin receptor in 3T3-L1 adipocytes is regulated primarily by its intracellular concentration and not by the state of occupancy of internalized receptor.

Calcitonin gene-related peptide (CGRP) immunoreactivity in the neuroendocrine Merkel cells and nerve fibres of pig and human skin

The presence of calcitonin gene-related peptide (CGRP) in the skin of pig snout and human fingertip was investigated using immunohistochemical techniques. CGRP immunoreactivity was found in Merkel cells and nerve fibres of both species. In pig snout skin, Merkel cells containing CGRP were seen forming clusters at the tips of rete ridge epidermis and in the external root sheath of sinus hair follicles (vibrissae). Human Merkel cells immunostained for CGRP were found isolated or forming small groups in the basal layer of glandular epidermal ridges. In all cases, immunoreactivity was more intense on the side of the Merkel cell facing the associated nerve terminal (which was never positive for CGRP). This part of the Merkel cell has the greatest density of dense-cored granules, suggesting that CGRP must be stored in these granules. Nerve bundles containing CGRP-immunoreactive fibres were found at dermal and hypodermal level, and blood vessels were often surrounded by CGRP nerve fibres. In pig snout skin some nerve fibres containing CGRP penetrated the epidermis and terminated as free endings, and in the human fingertip a small number of CGRP-immunoreactive nerve fibres were seen in Meissner's corpuscles.

Changes in purine nucleoside phosphorylase activity during thymosin-induced human null cell differentiation

Purine nucleoside phosphorylase (PNP) is a purine salvage pathway enzyme which we have found to be 8-10 times more active (per cell) in human peripheral blood null lymphocytes than in T lymphocytes. To test the hypothesis that null cells are, in part, pre-T lymphocytes we have defined an in vitro system for null cell differentiation into T cells and examined PNP activity during this differentiation process. We found that about 10% of human null cells could be driven to differentiate into T cells using thymosin fraction 5 (TF5) an extract of bovine thymus glands. The response to TF5 was dose related to up to 250 micrograms/ml with a maximum response occurring by 42-46 hr incubation. Exposure to TF5 was necessary for more than 4 hr but no more than 8 hr in order to obtain a maximum response. Both OKT4 and OKT8 positive cells were present in the newly differentiated T cell population but OKT8 positive cells appeared to predominate (OKT4/OKT8 = 0.698 +/- 0.30, mean +/- 1 SD). The differentiation process did not involve DNA synthesis but was inhibited at 4 degrees C. In the newly differentiated T cells PNP activity per cell was 8- to 10-fold lower (36 +/- 23 nm/hr/106 cells) than in null cells (311 +/- 136), and was at a level similar to mature T cells (56 +/- 7). Thus, human peripheral blood null cells can be induced to differentiate into T lymphocytes which can be characterized by both surface markers and biochemical parameters. Future studies will look at the function of TF5-induced T cells and the regulation of PNP activity during the differentiation process.