Assessment of Right Ventricular Systolic Function using Tricuspid Annular Plane Systolic Excursion (TAPSE) among HIV Patients on HAART and Its Relationship with Viral Load and CD4 Cell Count

BACKGROUND

The introduction of highly active antiretroviral therapy (HAART) has decreased the morbidity and mortality associated with HIV infection; however, this survival advantage is not free from complications. HIV patients are more likely to develop cardiovascular disease compared with the general population, and right ventricular systolic dysfunction is said to be associated with worse outcomes. We, therefore, sought to assess right ventricular systolic function using tricuspid annular plain systolic excursion (TAPSE) among HIV patients on HAART and its relationship with viral load and CD4 cell count.

METHODS

The study was a cross-sectional conducted among HIV patients receiving HAART at the Federal Medical Centre, Nguru, Yobe State, Northeastern Nigeria. Right ventricular systolic function was assessed using tricuspid annular plane systolic excursion.

RESULTS

One hundred and seven (107) subjects were recruited into the study comprising thirty-seven (34.6%) males and seventy (65.4%) females. The mean CD4 cell count and viral load of the studied patients were 612.65 ± 347.62 cells/μL and 315.44±271.11copies/mL, respectively. The distribution of RVSF according to CD4 cell count showed, fifteen (14.01%) patients with CD4 cell count less than 250 had reduced right ventricular systolic function (RVSF), 30 (28.03%) patients with CD4 cell count 250 - 500 had reduced RVSF, 1 (0.93%) patient with CD4 cell count 250 - 500 had normal RVSF, 47 (43.92%) patients with CD4 cell count 501 -1,000 had normal RVSF and 14(13.08%) patients with CD4 cell count greater than 1,000 had normal RVSF. Fourteen (13.08%) patients with undetectable viral load had normal RVSF, 47(43.92%) patients with viral load 50 - 1,500 had normal RVSF, 1(0.93%) patient with viral load 1,501 - 10,000 had normal RVSF, 30(28.03%) patients with viral load 1,501 - 10,000 had reduced RVSF and 15(14.01%) patients with viral load 10,000 - 50,000 had reduced RVSF. There was a positive and significant correlation between tricuspid annular plain systolic excursion with CD4 cell count and a negative but significant correlation HIV viral load.

CONCLUSION

We therefore concluded that asymptomatic right ventricular systolic dysfunction exists among patients with HIV infection and there was positive and significant correlation between tricuspid annular plain systolic excursion with CD4 cells count and a negative but significant correlation HIV viral load.

Prevalence of Doppler-Derived Left Ventricular Diastolic Dysfunction Among Newly Diagnosed Hypertensive Patients

BACKGROUND

The initial sign of hypertensive heart disease (HHD) is left ventricular diastolic dysfunction (LVDD), which is caused by remodeling of the left ventricle and left atrium, resulting in impaired relaxation of the left ventricle. LVDD is also partly due to left ventricular hypertrophy (LVH). If left untreated, LVDD can progress to diastolic heart failure and systolic heart failure. In Western countries, the prevalence of LVDD in long-term hypertensive patients ranges from 40.3% to 60%, but it is more common among hypertensive Nigerians. Since systemic hypertension can be asymptomatic in the early stages, it is important to evaluate LVDD early and control blood pressure to slow down its progression.

AIMS AND OBJECTIVES

The study aims to highlight the prevalence of LVDD and to determine the stages of LVDD among newly diagnosed hypertensive patients at the University of Maiduguri Teaching Hospital (UMTH).

METHOD

The study design is a hospital-based, cross-sectional, observational study. The study population consists of 352 consecutive treatment Naïve hypertensive adult patients aged 18 years and above who presented to the Cardiology Clinic of UMTH from June 2019 to June 2021. The study used the diagnostic criteria for LVDD and LVH which were based on the American Society of Echocardiography and the European Association of Cardiovascular Imaging.

RESULTS

A total of 352 newly diagnosed hypertensive patients were recruited, with a mean age of 50.9 ± 11.8 years, and 54.3% were female. The majority of patients (63.6%) were overweight or obese, with a mean body mass index (BMI) of 28.5 ± 4.6 kg/m2. The mean systolic blood pressure (SBP) was 155.7 ± 16.9 mmHg, and the mean diastolic blood pressure (DBP) was 92.8 ± 10.8 mmHg. LVDD was found in 58.5% of the patients, with stage 1 LVDD being the most common (42.6%), followed by stage 2 LVDD (15.9%). The prevalence of LVDD was significantly higher in females compared to males. Patients with LVDD were significantly older and had higher BMI, higher systolic and DBP, higher pulse pressure, higher LAVI, and higher LVMI compared to those without LVDD (P < 0.05).

CONCLUSION

LVDD is highly prevalent among newly diagnosed hypertensive patients, with stage 1 being the most common. Female gender, older age, higher BMI, higher blood pressure, higher LAVI, and higher LVMI were significant predictors of LVDD. Early detection and appropriate management of LVDD may help to prevent adverse cardiovascular outcomes in hypertensive patients.

Echocardiographic Left Ventricular Hypertrophy and Geometric Patterns in Patients with Sickle Cell Anaemia

BACKGROUND

Left ventricular hypertrophy (LVH) is a common complication in patients with sickle cell anaemia (SCA), and it has been associated with systolic and diastolic dysfunction, and sudden death. There is a wide variation in the reported prevalence of LVH in patients with SCA, partly due to the varying criteria applied, and the impact of small weight and body surface area (BSA) in SCA patients. We used four different criteria to determine echocardiographic LVH and geometric patterns in patients with steady-state SCA. Left ventricular hypertrophy was defined by LVM, LVM indexed to BSA, LVM indexed to height and LVM indexed to height2.7 using gender-specific reference values. Left ventricular geometry was determined using LVH and relative wall thickness.

RESULTS

Eighty-two patients with steady-state SCA, aged 18years and above were studied from January 2018 to April 2018. The median [IQR] age of the patients was 23 [10] years. Forty-seven (57.3%) were females. The prevalence of LVH was highest when LVM was indexed to BSA (80.5%), followed by LVM indexed to height (73.2%). Comparable prevalences of 68.3% and 69.5% were observed using LVM and LVM indexed to height2.7, respectively. The prevalence of LVH was similar in males and females for all the criteria.

CONCLUSION

The prevalence of LVH is high among patients with steady-state SCA irrespective of the criteria applied. The most prevalent geometric pattern was eccentric LVH. Indexing to BSA might result in over-estimation of LVH given the relatively small BSA in patients with SCA. Indexing to height 2.7 might give a more accurate estimate of LVH.

Influence of systolic blood pressure on outcomes in Nigerians with peripartum cardiomyopathy

BACKGROUND

The relationship between blood pressure (BP) trajectories and outcomes in patients with peripartum cardiomyopathy (PPCM) is not clear. Aim: The study aimed to assess the clinical features and outcomes (all-cause mortality and unrecovered left ventricular [LV] systolic function) of PPCM patients grouped according to their baseline systolic BP (SBP).

PATIENTS AND METHODS

PPCM patients presenting to 14 tertiary hospitals in Nigeria were consecutively recruited between June 2017 and March 2018 and then followed up till March 2019. SBP at first presentation was used to categorize the patients into seven groups: <90, 90-99, 100-109, 110-119, 120-129, 130-139, and ≥140 mmHg. Unrecovered LV systolic function was defined as echocardiographic LV ejection fraction (LVEF) below 55% at the last profiling.

RESULTS

Two hundred and twenty-seven patients were recruited and followed up for a median of 18 months. Of these, 4.0% had <90 mmHg, 16.3% had 90-99 mmHg, 24.7% had 100-109 mmHg, 24.7% had 110-119 mmHg, 18.5% had 120-129 mmHg, 7.5% had 130-139 mmHg, and 4.4% had ≥140 mmHg of SBP at presentation. The highest frequency of all-cause mortality was recorded among patients with SBP ≤90 mmHg (30.8%) followed by those with 90-99 mmHg (20.5%) (P = 0.076), while unrecovered LV systolic function did not differ significantly between the groups (P = 0.659). In a Cox proportional regression model for all-cause mortality, SBP <90 mmHg had a hazard ratio (HR) of 4.00 (95% confidence interval [CI] 1.49-10.78, P = 0.006), LVEF had an HR of 0.94 (95% CI 0.91-0.98, P = 0.003, B = 0.06%), and use of angiotensin-converting enzyme or angiotensin receptor and/or β-receptor blockers had an HR of 1.71 (95% CI 0.93-3.16, P = 0.085). However, SBP was not associated with LV function recovery.

CONCLUSION

In our cohort of PPCM patients, one-fifth was hypotensive at presentation. SBP <90 mmHg at presentation was associated with a four-fold higher risk of all-cause mortality during a median follow-up of 18 months.

Impact of Climate Change on Management of Systemic Hypertension in North-Eastern Nigeria

The impact of climate change on health, including changes in epidemiology and heat-related complications, has been variously reported in many parts of the world. Maiduguri, the capital of Borno state in north-eastern Nigeria, has been bearing the brunt of increasing temperatures over the past years, especially during the early months of the year building up to the commencement of the rainy season; with an average daily temperature forecasted to be around 40C. Patients with systemic hypertension and other forms of cardiovascular diseases are vulnerable to heat-related complications including dehydration, hypotension, and orthostatic hypotension (OH). This is particularly true in patients receiving various forms of antihypertensive medication, including diuretics. We present three cases of symptomatic OH occurring during the peak of heat season in Maiduguri among patients receiving various combinations of antihypertensive medication. L'impact du changement climatique sur la santé, y compris les changements dans l'épidémiologie et les complications liées à la chaleur, a été diversement rapporté dans de nombreuses régions du monde. Maiduguri, la capitale de l'État de Borno, dans le nord-est du Nigeria, a subi de plein fouet l'augmentation des températures au cours des dernières années, en particulier au cours des premiers mois de l'année, jusqu'au début de la saison des pluies. Les patients souffrant d'hypertension systémique et d'autres formes de maladies cardiovasculaires sont vulnérables aux complications liées à la chaleur, notamment la déshydratation, l'hypotension et l'hypotension orthostatique (OH). Cela est particulièrement vrai chez les patients recevant diverses formes de médicaments antihypertenseurs, notamment des diurétiques. Nous présentons trois cas d'OH symptomatique survenus pendant le pic de la saison chaude à Maiduguri chez des patients recevant diverses combinaisons de médicaments antihypertenseurs. Mots clés: Changement climatique, Hypertension, Agents antihypertenseurs, Hypotension orthostatique, Zone semiaride, Maiduguri, Nigeria.

Relationship between CD4 Cell Count, Viral Load and Left Ventricular Function among HIV-1 Infected Patients Asymptomatic for Cardiac Disease on HAART

INTRODUCTION

Human immunodeficiency virus (HIV) infected patients are at increased risk for myocardial infarction and cardiomyopathy. Low CD4 cell count and high viral load were identified as independent risk factors for cardiac disease. Asymptomatic cardiac dysfunction has also been reported in HIV-infected individuals.

METHODS

This was a cross-sectional study conducted among consecutive HIV patients who are asymptomatic for cardiac disease receiving highly active antiretroviral therapy (HAART) at the ART clinic of Federal Medical Centre Nguru, Yobe State Northeastern Nigeria.

DATA ANALYSIS

Statistical analysis was done using SPSS version 21.0 (SPSS IBM) Chicago Illinois. Data were presented as mean ± standard deviation (SD) for continuous variables, while categorical variables were expressed as frequencies and proportions. Correlation and regression analyses were done to determine the relationship between CD4 cell count, viral load and left ventricular function. A p-value of d"0.05 was considered significant.

RESULTS

Patients with high CD4 cells count (>500 cells/µL) were found to have preserved left ventricular systolic function while those with low CD4 cells count (500 cells/μL while those with low CD4 cell count (1500 copies/mL) were associated with reduced left ventricular systolic function and severe diastolic dysfunction. We therefore suggest that there is need for early evaluation of left ventricular function in HIV patients before developing symptoms of cardiac decompensation.

Incidence, clinical characteristics, and risk factors of peripartum cardiomyopathy in Nigeria: results from the PEACE Registry

Aims

The aim of this study was to describe the incidence, clinical characteristics and risk factors of peripartum cardiomyopathy (PPCM) in Nigeria.

Methods and Results

The study was conducted in 22 hospitals in Nigeria, and PPCM patients were consecutively recruited between June 2017 and March 2018. To determine factors associated with PPCM, the patients were compared with apparently healthy women who recently delivered, as controls. Four hundred six patients were compared with 99 controls. The incidence and disease burden (based on the rate of consecutive recruitment of subjects) varied widely between the six geographical zones of Nigeria. From the North–West zone, 72.3% of the patients was recruited, where an incidence as high as 1 per 96 live births was obtained in a centre, while the disease was uncommon (7.6% of all recruited patients) in the South. Majority of the patients (76.6%) and controls (74.8%) (p = 0.694) were of Hausa–Fulani ethnic group. Atrial fibrillation, intracardiac thrombus, stroke, and right ventricular systolic dysfunction were found in 1.7%, 6.4%, 2.2%, and 54.9% of the patients, respectively. Lack of formal education (odds ratio [OR] 3.08, 95% confidence interval [1.71, 5.53]; P < 0.001), unemployment (OR: 3.28 [2.05, 5.24]; P < 0.001), underweight (OR: 13.43 [4.17, 43.21]; P < 0.001) and history of pre‐eclampsia (OR: 9.01 [2.18, 37.75]; P = 0.002) emerged as independent PPCM risk factors using regression models. Customary hot baths (OR: 1.24 [0.80, 1.93]; P = 0.344), pap enriched with dried lake salt (OR: 1.20 [0.74, 1.94]; P = 0.451), and Hausa–Fulani ethnicity (OR: 1.11 [0.67, 1.84]; P = 0.698) did not achieve significance as PPCM risk factors.

Conclusions

In Nigeria, the burden of PPCM was greatest in the North–West zone, which has the highest known incidence. PPCM was predicted by sociodemographic factors and pre‐eclampsia, which should be considered in its control at population level. Postpartum customary birth practices and Hausa–Fulani ethnicity were not associated with PPCM in Nigeria.

Status of cardiac arrhythmia services in Africa in 2018: a PASCAR Sudden Cardiac Death Task Force report

Background

There is limited information on the availability of health services to treat cardiac arrhythmias in Africa.

Methods

The Pan–African Society of Cardiology (PASCAR) Sudden Cardiac Death Task Force conducted a survey of the burden of cardiac arrhythmias and related services over two months (15 October to 15 December) in 2017. An electronic questionnaire was completed by general cardiologists and electrophysiologists working in African countries. The questionnaire focused on availability of human resources, diagnostic tools and treatment modalities in each country.

Results

We received responses from physicians in 33 out of 55 (60%) African countries. Limited use of basic cardiovascular drugs such as anti–arrhythmics and anticoagulants prevails. Non–vitamin K–dependent oral anticoagulants (NOACs) are not widely used on the continent, even in North Africa. Six (18%) of the sub–Saharan African (SSA) countries do not have a registered cardiologist and about one–third do not have pacemaker services. The median pacemaker implantation rate was 2.66 per million population per country, which is 200–fold lower than in Europe. The density of pacemaker facilities and operators in Africa is quite low, with a median of 0.14 (0.03–6.36) centres and 0.10 (0.05–9.49) operators per million population. Less than half of the African countries have a functional catheter laboratory with only South Africa providing the full complement of services for cardiac arrhythmia in SSA. Overall, countries in North Africa have better coverage, leaving more than 110 million people in SSA without access to effective basic treatment for cardiac conduction disturbances.

Conclusion

The lack of diagnostic and treatment services for cardiac arrhythmias is a common scenario in the majority of SSA countries, resulting in sub–optimal care and a subsequent high burden of premature cardiac death. There is a need to improve the standard of care by providing essential services such as cardiac pacemaker implantation.

Prevalence of overweight and obesity in Maiduguri, North-Eastern Nigeria

BACKGROUND

The prevalence of obesity is on the increase worldwide including in many developing countries. There is no report on the magnitude of obesity among adults in Maiduguri, a major city in northeastern Nigeria.

MATERIALS AND METHODS

We selected a sample of 1650 men and women aged 15 years and above resident in Gwange ward in Maiduguri metropolitan council using a multistage sampling technique. Height, weight, waist (WC) and hip circumferences w measured. Body mass index (BMI) and waist-to-hip ratio (WHR) were calculated. Data were analyzed using SPSS version13. The ethics committee of the University of Maiduguri Teaching Hospital approved the study and consent was sought individually from the participants before being enlisted.

RESULTS

The mean (SD) age of the respondents was 36.2 (14.4) years, with a range of 15 to 70 years. The mean (SD) ages of the males and females were 34.9 4.3) and 38.9 (14.0) years, respectively, (p < 0.001). The overall crude prevalence rates of overweight and obesity were 27.1% and 17.1%, respectively. In men, 40.6% were either overweight or obese, while in women 51.9% were either overweight or obese. We observed the highest prevalence rates of overweight and obesity in the middle age group. There were more obese females than males (14.05 vs. 4.3%) among both young and elderly (12.1% vs. 10.5%) subjects.

CONCLUSION

The prevalence of overweight and obesity is high in Maiduguri metropolis particularly among women. Concerted efforts should be made to curb the menace of increasing rate of obesity in the metropolis through public enlightenment on the risks associated with obesity and the benefits of adopting a healthy lifestyle.

Left ventricular geometry in Nigerians with type II diabetes mellitus

BACKGROUND

Left ventricular hypertrophy is independently associated with increased incidence of cardiovascular disease, cardiovascular and all cause mortality. In a relatively healthy hypertensive adult population, type II diabetes is associated with higher left ventricular mass, concentric left ventricular geometry and lower myocardial function independent of age, sex, body size, and arterial blood pressure.

OBJECTIVE

The study is to investigate left ventricular geometry in Nigerians with Type II Diabetes mellitus.

METHODS

The study design was cross-sectional and it comprised 75 consecutive patients with type II diabetes mellitus with or without hypertension. Using a structured pre-evaluated questionnaire, the demographic and clinical data were obtained. All subjects had two dimensional (2D) and 2D derived M-mode echocardiography using Sonoline G60s Ultrasound imaging system with 4.2 MHZ transducer equipped with simultaneous ECG tracing.

RESULTS

A total of 75 consecutive type II diabetic patients with or without hypertension were recruited into the study. There were 18 (24.0%) hypertensive-diabetic and 12 (16.0%) normotensive-diabetic males and Thirty-four (45.3%) hypertensive-diabetic and 11 (14.0%) normotensive-diabetic were females. Hypertensive-diabetic males had significantly higher left ventricular mass compared to normotensive-diabetic counterpart 207.05 +/- 41.5g and 156.00 +/- 27.1g P = 0.001. Similarly, left ventricular mass index was found to be higher in hypertensive-diabetic males than their normotensive-diabetic counterpart 114.50 +/- 29.2g/m2 and 92.28 +/- 20.5g/m2 P = 0.014. Hypertensive-diabetic female significantly had higher LVM compared to the normotensive-diabetics 196.06 +/- 41.5g and 161.54 +/- 31.6g P = 0.016. Left ventricular mass index was also found to be higher in hypertensive-diabetic female than their normotensive counterpart 118.52 +/- 27.8g/m2 and 95.75 +/- 23.0g/m2 P = 0.019. Hypertensive-diabetics had predominantly concentric left ventricular hypertrophy compared to the normotensive-diabetics 36 (69.2. %) and 5 (21.7%) P = 0.001.

CONCLUSION

The study reported that hypertensive-diabetics have predominantly concentric left ventricular hypertrophy, higher left ventricular mass and left ventricular mass index compared to normotensive-diabetic. Female hypertensive-diabetic had predominantly concentric left ventricular hypertrophy, while male hypertensive-diabetic and normotensive-diabetic had predominantly concentric left ventricular remodelling.

Detergent-salt resistance of LAP2alpha in interphase nuclei and phosphorylation-dependent association with chromosomes early in nuclear assembly implies functions in nuclear structure dynamics

Lamina-associated polypeptide (LAP) 2 of the inner nuclear membrane (now LAP2beta) and LAP2alpha are related proteins produced by alternative splicing, and contain a common 187 amino acid N-terminal domain. We show here that, unlike LAP2beta, LAP2alpha behaved like a nuclear non-membrane protein in subcellular fractionation studies and was localized throughout the nuclear interior in interphase cells. It co-fractionated with LAP2beta in nuclear lamina/matrix-enriched fractions upon extraction of nuclei with detergent, salt and nucleases. During metaphase LAP2alpha dissociated from chromosomes and became concentrated around the spindle poles. Furthermore, LAP2alpha was mitotically phosphorylated, and phosphorylation correlated with increased LAP2alpha solubility upon extraction of cells in physiological buffers. LAP2alpha relocated to distinct sites around chromosomes at early stages of nuclear reassembly and intermediarily co-localized with peripheral lamin B and intranuclear lamin A structures at telophase. During in vitro nuclear assembly LAP2alpha was dephosphorylated and assembled into insoluble chromatin-associated structures, and recombinant LAP2alpha was found to interact with chromosomes in vitro. Some LAP2alpha may also associate with membranes prior to chromatin attachment. Altogether the data suggest a role of LAP2alpha in post-mitotic nuclear assembly and in the dynamic structural organization of the nucleus.

Whole blood culture for measuring mitogen induced T cell proliferation provides superior correlations with disease state and T cell phenotype in asymptomatic HIV-infected subjects

Proliferative responses to a panel of mitogens were compared in parallel for two sources of cells, whole blood (WB) and conventionally prepared peripheral blood mononuclear cells (PBMC), obtained from asymptomatic HIV seropositive and control subjects. Weak but statistically significant correlations of the proliferative responses were observed. Use of either lymphocyte source produced significant differences in the proliferative responses between the HIV seropositive and control subjects, but the use of WB was more powerful, with a smaller sample size being required to discriminate between the proliferative responses of the two study groups. Furthermore, proliferative responses using WB gave strong and highly significant correlations with a number of important changes in the surface marker phenotype of the lymphocyte populations in the HIV seropositive subjects including CD4, CD8, CD4:CD8 ratio and certain CD8 subsets, whereas strong correlations were not observed with the PBMC. The response of WB lymphocytes to staphylococcal enterotoxin B (SEB) was highly reproducible and provided the best discrimination between HIV-infected and control subjects. We conclude that the use of WB for measuring lymphoproliferation is easy, rapid, accurate, and discriminative for assessing and following the changes in immune function which occur in HIV seropositive subjects, applicable in the clinical as well as in the research setting.

Immunosuppression by glucocorticoids: inhibition of production of multiple lymphokines by in vivo administration of dexamethasone

Glucocorticoids are extremely potent immunosuppressive agents, capable of directly affecting the function of lymphocytes. We studied the effect of in vivo dexamethasone (DEX) administration on anti-CD3-induced lymphocyte proliferation and lymphokine production in mice. To characterize the kinetics and dose responsiveness of lymphocytes to DEX, splenocytes from BALB/c mice that had received a single dose of DEX in vivo were cultured in vitro with suboptimal and optimal concentrations of anti-CD3 monoclonal antibody. Cell proliferation in response to suboptimal concentrations of anti-CD3 was decreased by DEX doses of > or = 30 mg/kg; much higher doses (> or = 200 mg/kg) were required to inhibit cell proliferation in response to optimal anti-CD3 stimulation. Inhibition of suboptimal anti-CD3-stimulated proliferation was evident within 4 hr after DEX administration, was maintained for at least 24 hr, and was no longer evident at 7 and 14 days. Lymphokine secretion induced by optimal doses of anti-CD3 in vitro was differentially affected by in vivo DEX treatment. IL-1 alpha, IL-4, IL-6, IL-10, and IFN-gamma levels were decreased by treatment with low doses of DEX (30 mg/kg), whereas higher doses were required to inhibit production of IL-2, IL-3, and TNF. GM-CSF (granulocyte-macrophage-colony stimulating factor) was least susceptible to DEX inhibition. Low-dose (30 mg/kg) DEX treatment significantly reduced anti-CD3-stimulated production of most lymphokines tested at 4 and 12 hr; by 24 hr the levels of most lymphokines had begun to return to control values. Hence, our data indicate that administration of a single dose of DEX (30 mg/kg for 4 hr) results in significant suppression of lymphokine production and cell proliferation that precedes any significant cell loss and can be used as a reversible model of immunosuppression.

Identification of anti-CD3 antibodies that do not modulate antigen but induce mitogenesis and block the mixed lymphocyte reaction

Using a panel of anti-CD3-TCR monoclonal antibodies (OKT3 A-E), it appears possible to separate the ability to cause surface antigen modulation from inhibition of MLR or induction of mitosis. OKT3D, an antibody that recognizes the CD3 antigen at a site that can be differentiated from the epitopes recognized by other members of this panel by competition binding, does not cause antigen modulation when incubated with human T cells for up to 3 days. Despite this, OKT3D is mitogenic and is capable of blocking MLR. Two different isotypes were produced from the OKT3D clone, IgG1 and IgG2b. The IgG2b isotype of OKT3D blocked MLR even in individuals unable to respond mitogenically to this antibody. Use of members of this panel may now permit dissection of the types of signals delivered by the CD3-TCR complex inducing mitosis, receptor modulation, and other T-cell responses.

Use of monoclonal antibodies to identify thymopoietin in cultured human thymic epithelial cells

Murine monoclonal antibodies (mAbs) were developed to discriminate thymopoietin, a human thymic hormone, and thysplenin, a closely related molecule found in spleen. Three of these recognized both native and synthetic thymopoietin as well as thysplenin. Together they define two non-overlapping epitopes which withstand sodium dodecyl sulfate denaturation and can be detected by western blotting. We used these three mAbs to demonstrate the production of thymopoietin by cultured thymic epithelial cells for up to several weeks. Three additional mAbs were selective for thysplenin. Highly specific mAbs will be useful for characterizing further these physiologically distinct polypeptides.

OKT3E, an anti-CD3 antibody that does not elicit side effects or antiidiotype responses in chimpanzees

Chimpanzees were injected with OKT3 and two other anti-CD3 antibodies, OKT3D and OKT3E. Both of the new antibodies were of the mouse IgG2b isotype. Administration of the antibodies was identical to the clinical regimen used for OKT3 in humans: 5 mg i.v., daily for 10 consecutive days. All animals were monitored for fever during administration of the antibodies, and blood samples were taken throughout the treatment period for monitoring the effects of the antibodies on peripheral lymphocyte subsets and the appearance of circulating cytokines. OKT3 produced similar clinical effects to those observed in humans; fever (2/3), as well as elevations in cytokines were observed. As in humans, peripheral T cells were cleared with the first dose and remained absent or modulated of their T cell receptor molecules throughout treatment. OKT3D, IgG2b also produced fevers (2/3) and elevations of cytokines. Although it also cleared circulating T cells with the first dose and T cell counts remained low throughout treatment, remaining circulating T cells were coated with administered antibody and were able to reexpress the CD3 antigen. OKT3E, IgG2b produced no temperature elevations and no elevations in cytokines. Although it cleared the circulation of T cells with the first does, cells reappeared during treatment, modulated of their CD3 antigens or coated with the administered antibody. All three antibodies raised antimouse antibodies, and OKT3 and OKT3D also produced blocking antiidiotype antibodies. OKT3E treatment did not result in anti-OKT3E blocking antibodies.

Flow cytometric resonance energy transfer measurements support the association of a 95-kDa peptide termed T27 with the 55-kDa Tac peptide

Two monoclonal antibodies (OKT27 and OKT27b) have been produced that react with distinct epitopes of a 95-kDa peptide. The T27 antigen is widely distributed, being expressed on B lymphocytes, monocytes, and adult T-leukemic cells but not on polymorphonuclear leukocytes or platelets. There was a low level of T27 expression on resting T cells that increased on T-cell activation. In preliminary studies, the OKT27b antibody coprecipitated a 55-kDa peptide, as well as the 95-kDa peptide, from the radiolabeled cells of the HuT 102B2 cell line. Preclearance with anti-Tac, a monoclonal antibody to the 55-kDa peptide of the multichain interleukin 2 receptor, removed the 55-kDa but not the 95-kDa peptide from subsequent OKT27b immunoprecipitates of HuT 102B2 extracts, suggesting the possibility that the T27 peptide was associated with the Tac peptide. However, the precipitation of the p55 Tac peptide by OKT27b was quite inconsistent. Thus, additional information was sought using a flow cytometric energy transfer technique to provide a physical estimation of the proximity between the Tac and the T27 peptides. The flow cytometric version of the fluorescence resonance energy transfer technique permits the determination of inter- and intramolecular distances at 2- to 10-nm levels on a cell-by-cell basis. Using this approach, there was a mean energy transfer of 7.3% with HuT 102B2 cells when fluorescein isothiocyanate anti-Tac served as the donor and tetramethylrhodamine isothiocyanate OKT27 served as the acceptor. In contrast, there was no energy transfer in comparable studies observed when fluorescein anti-Tac and rhodamine anti-transferrin receptor antibodies were used. These observations support the conclusion that there is a close nonrandom proximity in HuT 102B2 cells between the 95-kDa peptide identified by the OKT27 monoclonal antibody and the p55 Tac peptide of the multichain interleukin 2 receptor.

Functional interaction between human T-cell protein CD4 and the major histocompatibility complex HLA-DR antigen

Mature T cells segregate phenotypically into one of two classes: those that express the surface glycoprotein CD4, and those that express the glycoprotein CD8. The CD4 molecule is expressed primarily on helper T cells whereas CD8 is found on cytotoxic and suppressor cells. A more stringent association exists, however, between these T-cell subsets and the major histocompatibility complex (MHC) gene products recognized by their T-cell receptors (TCRs). CD8+ lymphocytes interact with targets expressing class I MHC gene products, whereas CD4+ cells interact with class II MHC-bearing targets. To explain this association, it has been proposed that these 'accessory' molecules bind to monomorphic regions of the MHC proteins on the target cell, CD4 to class II and CD8 to class I products. This binding could hold the T cell and its target together, thus improving the probability of the formation of the trimolecular antigen: MHC: TCR complex. Because the TCR on CD4+ cells binds antigen in association with class II MHC, it has been difficult to design experiments to detect the association of CD4 with a class II molecule. To address this issue, we devised a xenogeneic system in which human CD4 complementary DNA was transfected into the murine CD4-, CD8- T-cell hybridoma 3DT-52.5.8, the TCR of which recognizes the murine class I molecule H-2Dd. The murine H-2Dd-bearing target cell line, P815, was cotransfected with human class II HLA-DR alpha, beta and invariant chain cDNAs. Co-culture of the parental T-cell and P815 lines, or of one parental and one transfected line resulted in a low baseline response. In contrast, a substantial increase in response was observed when CD4+ 3DT-52.5.8 cells were co-cultured with HLA-DR+ P815 cells. This result strongly indicates that CD4:HLA-DR binding occurs in this system and that this interaction augments T-cell activation.

Null cell identification and characterization with OKT16: an anti-p40 monoclonal antibody

A murine monoclonal antibody, OKT16, specific for human lymphocytes of T lineage, was isolated by standard immunization and hybridization techniques. The distribution of the antigen defined by OKT16 was similar to the antigen reactive with monoclonal antibodies 3A1 and WT1. This identity of antigen targets was confirmed in an enzyme-linked immunosorbent assay system and by sequential immunoprecipitation. Under reducing conditions, OKT16 reacted with an antigen of 40K daltons; however, under nonreducing conditions this antigen appeared as an 84K-dalton molecule, which suggests that the p40 antigen exists as a disulfide-linked dimer. By indirect immunofluorescence, OKT16 reacted with a greater fraction of nonrosetting, non-B (null) lymphocytes than with antibodies to other T cell-specific proteins. Two-color immunofluorescence demonstrated the coexpression of the T16 antigen and the C3bi receptor on most null cells. The T10 antigen (found on cortical thymocytes and activated peripheral T cells) was restricted to most T16-bearing null cells and expression of the Fc receptor for aggregated IgG (defined by monoclonal antibody 73.1) was restricted to a major subset of T16-bearing null cells. The T cell-specific markers defined by OKT8, OKT11, and OKT17, as well as the monocyte marker defined by OKM5, were expressed by smaller subsets of OKT16-reactive null cells. These studies support by phenotypic analysis the functional heterogeneity ascribed to null cells. The 40K-dalton T16 antigen has the most extensive null cell representation of all the T lineage markers described to date.

Thymopoietin radioreceptor assay utilizing lectin-purified glycoprotein from a biologically responsive T cell line

Radiolabeled thymopoietin that was biologically active and of high specific activity was prepared by a novel technique involving protection of free amino groups, selective excision of the protected N-terminal prolyl group with post-proline cleaving enzyme, reaction of the newly exposed alpha-amino group with a highly radioiodinated compound, and deprotection and purification of the polypeptide. Binding of this radiolabeled thymopoietin was not demonstrable by conventional techniques with cells, cell membranes, or solubilized cell membranes, apparently due to the presence of active proteases in these preparations. A glycoprotein with thymopoietin binding properties was prepared by lectin purification from the detergent-solubilized membranes of CEM cells, a human T cell line that responds to thymopoietin in vitro with increases in intracellular cyclic GMP. Presumably this procedure separated the thymopoietin binding protein from membrane proteases, thus permitting the development of a radioreceptor assay. Evidence is presented that the thymopoietin binding protein represents a thymopoietin receptor that is probably related to the mediation of immunoregulatory actions of thymopoietin on a subset of peripheral T cells.

Distinct classes of human T-cell activation antigens

The characterization of three groups of antigens expressed by activated human T lymphocytes and detected by monoclonal antibodies is reported. Antigens defined by OKT19, OKT21, and OKT22 do not appear on in vitro activated T cells until increases in DNA synthesis become apparent and are not detected on most Interleukin 2 (IL-2)-independent cell lines and normal peripheral blood lymphocytes, monocytes, and granulocytes. Cell surface molecules reactive with the monoclonal antibodies OKT23 and OKT24 are displayed prior to any notable increase in DNA synthesis and are present on IL-2 independent cell lines, irrespective of lineage. T23 and T24 do not appear on peripheral blood cells and their distribution more closely resembles that of the T9 antigen (the receptor for transferrin) than antigens of the other groups. The third group of antigens, T14 and T20, have been classified as "early" antigens relative to DNA synthesis. They are expressed by distinct populations of normal lymphoid cells as well as by some IL-2-independent cell lines. Display of each group of activation antigens on T lymphocytes can be induced by either phytohemagglutinin, purified protein derivative from tuberculin, or allogeneic non-T cells, is not restricted to the OKT4+ or OKT8+ subsets, and is predominant on cells exhibiting the light-scattering properties of blast cells. The relative lack of expression of these antigens among normal peripheral blood cells make them attractive candidates for identifying changes in the status of immune activation.

Distribution of antigens defined by OKB monoclonal antibodies on benign and malignant lymphoid cells and on nonlymphoid tissues

Monoclonal antibodies OKB1, OKB2, OKB4 and OKB7 have been previously shown to detect distinctive antigens displayed on B, but not on T, lymphocytes. Benign and malignant lymphoid cells were investigated for their reactivity with these antibodies in cell suspension by indirect immunofluorescence and in cryostat tissue sections by the avidin-biotin complex immunoperoxidase technique. Fetal liver pre-B cells and pre-B and common type acute lymphoblastic leukemia cells isolated from 15 patients were OKB1-OKB2+OKB4-OKB7-. All mature lymphoid tissue B cells and the neoplastic cell surface immunoglobulin-positive (SIg+) B cells isolated from each of 47 B cell neoplasms were OKB2+. OKB1 and OKB7 were expressed by interfollicular, follicular center, and many, but not all, mantle zone B cells. OKB4 was expressed by follicular center cells, but not by mantle zone or interfollicular B cells. The neoplastic SIg+ B cells isolated from 45 of 47 B cell malignancies were OKB1+OKB4+, and those isolated from 45 of 46 B cell malignancies were OKB7+. The neoplastic B cells of one mantle zone lymphoma were OKB1-, of one small lymphocytic cell lymphoma were OKB7-, of one large cell lymphoma were OKB4-, and of one small lymphocytic cell lymphoma with a monoclonal gammopathy were OKB1-OKB4-. Normal and myeloma plasma cells were OKB-. The malignant T cells isolated from 12 T cell neoplasms were OKB2-OKB4-, but were OKB1+ and/or OKB7+ in 3 cases. Thus, the OKB antibodies appear to detect distinctive antigens that may be expressed at different stages of B cell differentiation. In addition, OKB4 reacted with selected renal and respiratory epithelium, and OKB2 reacted with a wide range of epithelial tissues. The OKB antibodies should prove useful in the investigation of B cell differentiation and may aid in the identification and characterization of lymphoproliferative malignancies with significant therapeutic and prognostic differences not identifiable by conventional histopathologic and immunologic methods.

Possible involvement of the T4 molecule in T cell recognition of class II HLA antigens. Evidence from studies of CTL-target cell binding

The present study examines the potential role of the T4 molecule in functional cell-cell interactions between target cells and human cytotoxic T lymphocyte (CTL) clones that are specific for HLA class II alloantigens encoded by the SB locus. There were marked differences (greater than 30-fold) between the seven SB-specific clones studied with respect to their susceptibility to inhibition by anti-T4 as well as anti-T3 antibodies. We wished to test the hypothesis that such variation among the clones would be due to differences in clonal "affinity" for antigen. To quantitate differences among the CTL clones in the tightness with which they bind target cells, the clones were analyzed using a previously published assay of susceptibility of CTL-target cell conjugates to dissociation in the presence of unlabeled targets. The results revealed that the clones that were most susceptible to inhibition by anti-T4 and anti-T3 were the weakest target cell binders, and vice versa. Anti-T4 antibody could partially induce dissociation of functional CTL-target cell conjugates in the absence of any added cold targets. For the "highest affinity" clone such anti-T4 antibody-induced dissociation could be observed at 4 degrees C but not 23 degrees C. These results indicate that the T4 molecule is functionally involved in target cell binding by CTL, and raise the possibility that although it is easiest to demonstrate the function of the T4 molecule in "low affinity" clones, that function may also be operative in the "high affinity" clones.

The T4 surface antigen is involved in the induction of helper function

The OKT4 monoclonal antibody reacts with a 62K m.w. glycoprotein present on a subset of human T cells with the capacity to help or induce B cell differentiation. The present studies were undertaken to determine whether the T4 molecule itself plays any role in the helper function mediated by T4+ cells. Using a series of monoclonal antibodies (OKT4, OKT4A-E), which react with distinct noncompeting epitopes of the T4 molecule, we found that OKT4A and OKT4E, but not OKT4, antibodies inhibited the induction of B cell differentiation by T4+ cells. This inhibition was apparent when using nonirradiated or irradiated T4+ cells, and was noted over a wide range of concentrations. Importantly, inhibition occurred only if the antibody was present during the first 24 hr of cell culture, and the presence of antibody did not alter the kinetics of induction of B cell differentiation. Thus, these data suggest that the T4 molecule plays an early, critical role in cellular interactions required for helper cell function.

Distinct epitopes on the T8 molecule are differentially involved in cytotoxic T cell function

The present report attempts to determine if there are distinct epitopes on the T8 molecule that are involved in class I-restricted cytotoxic T lymphocyte (CTL) function. A panel of 9 monoclonal antibodies (OKT8A,B,C,E,F,G,H,I, and OKT5) was produced and all antibodies were shown to bind to the T8 molecule. This panel of antibodies was employed to characterize the distribution of distinct epitopes on the T8 molecule and to block the activity of class I-specific influenza virus-immune and allo-immune CTL effector function. Significant differences in the ability of the anti-T8 antibodies to block CTL function were observed: OKT8C and T8F blocked best (49 and 55% respectively); OKT8A,E,G,H,I, and OKT5 blocked less well (24-31%); and OKT8B blocked marginally (11%). There was no correlation between the capacity of the antibodies to block CTL function and their heavy chain isotype. Competitive binding of the different OKT8 antibodies to the cell surface and differential trypsin sensitivity of the epitopes recognized by the antibodies indicated that OKT8C and T8F were located on topographically distinct regions of the T8 molecule. These results indicate that specific epitopes on the T8 molecule are involved in CTL function, and that there could be more than one functional site on the molecule.

The T4 surface antigen is involved in the induction of helper function

The OKT4 monoclonal antibody reacts with a 62K m.w. glycoprotein present on a subset of human T cells with the capacity to help or induce B cell differentiation. The present studies were undertaken to determine whether the T4 molecule itself plays any role in the helper function mediated by T4+ cells. Using a series of monoclonal antibodies (OKT4, OKT4A-E), which react with distinct noncompeting epitopes of the T4 molecule, we found that OKT4A and OKT4E, but not OKT4, antibodies inhibited the induction of B cell differentiation by T4+ cells. This inhibition was apparent when using nonirradiated or irradiated T4+ cells, and was noted over a wide range of concentrations. Importantly, inhibition occurred only if the antibody was present during the first 24 hr of cell culture, and the presence of antibody did not alter the kinetics of induction of B cell differentiation. Thus, these data suggest that the T4 molecule plays an early, critical role in cellular interactions required for helper cell function.

Immunoassay for bovine serum thymopoietin: discrimination from splenin by monoclonal antibodies

A polyclonal rabbit anti-bovine thymopoietin antiserum was used to develop a radioimmunoassay and sandwich enzyme-linked immunosorbent (ELISA) assay for the thymic hormone thymopoietin. Both assays showed slightly less sensitivity for the closely related splenic hormone splenin (SP) than thymopoietin (TP) and markedly less sensitivity for the human as compared with the bovine polypeptides. A number of murine monoclonal antibodies specific for bovine thymopoietin were generated; they were unreactive with bovine splenin and were also unreactive with human thymopoietin and splenin. A sandwich ELISA using these monoclonal anti-TP antibodies together with polyclonal rabbit anti-TP was specific for bovine thymopoietin and measured 300-500 ng/ml thymopoietin in bovine serum. Similar approaches are being pursued to develop an immunoassay for thymopoietin in human serum.

Generation and characterization of monoclonal antibodies reactive with human B lymphocytes

Four novel monoclonal antibodies directed at determinants on human B lymphocytes were produced and characterized by flow cytometry using indirect immunofluorescence analysis. The antibodies, OKB1, OKB2, OKB4, and OKB7, define antigens not previously described on human B lymphocytes using B cell reactive monoclonal antibodies or standard B cell phenotypic markers. OKB4 [immunoglobulin M (IgM)] and OKB7 (IgG2a) were reactive with greater than 95% of all surface membrane immunoglobulin positive (Smlg+) lymphocytes and were restricted to the B cell lineage. OKB2 (IgG1) likewise reacted with greater than 95% of all Smlg+ lymphocytes; however, the antigen was also expressed on all granulocytes. In contrast to OKB2, OKB4, and OKB7, OKB1 reacted with a variable percentage of normal peripheral B cells (approximately 70 to 95%). Functional studies employing polyclonally activated B cells in a pokeweed mitogen (PWM) driven system and the reverse hemolytic plaque assay for the quantitation of Ig secreting plasma cells demonstrated that OKB1 and OKB2 inhibited the generation of plaque-forming cells (PFC) when added to cultures at day 0. OKB4 had a marginal inhibitory effect, whereas OKB7 consistently enhanced the PFC response. Immunoprecipitation studies with OKB1, OKB4, and OKB7 demonstrated that these antibodies precipitated antigens of approximately 168,000, 87,000, and 175,000 m.w., respectively. The OKB2 antigen is presently under study.

Generation and characterization of monoclonal antibodies reactive with human B lymphocytes

Four novel monoclonal antibodies directed at determinants on human B lymphocytes were produced and characterized by flow cytometry using indirect immunofluorescence analysis. The antibodies, OKB1, OKB2, OKB4, and OKB7, define antigens not previously described on human B lymphocytes using B cell reactive monoclonal antibodies or standard B cell phenotypic markers. OKB4 [immunoglobulin M (IgM)] and OKB7 (IgG2a) were reactive with greater than 95% of all surface membrane immunoglobulin positive (Smlg+) lymphocytes and were restricted to the B cell lineage. OKB2 (IgG1) likewise reacted with greater than 95% of all Smlg+ lymphocytes; however, the antigen was also expressed on all granulocytes. In contrast to OKB2, OKB4, and OKB7, OKB1 reacted with a variable percentage of normal peripheral B cells (approximately 70 to 95%). Functional studies employing polyclonally activated B cells in a pokeweed mitogen (PWM) driven system and the reverse hemolytic plaque assay for the quantitation of Ig secreting plasma cells demonstrated that OKB1 and OKB2 inhibited the generation of plaque-forming cells (PFC) when added to cultures at day 0. OKB4 had a marginal inhibitory effect, whereas OKB7 consistently enhanced the PFC response. Immunoprecipitation studies with OKB1, OKB4, and OKB7 demonstrated that these antibodies precipitated antigens of approximately 168,000, 87,000, and 175,000 m.w., respectively. The OKB2 antigen is presently under study.

Identification of the C3bi receptor of human monocytes and macrophages by using monoclonal antibodies

We have obtained four monoclonal antibodies, IB4, OKM1, OKM9, and OKM10, all directed against the C3bi receptor of human monocytes and macrophages (M phi). Two criteria were used to determine the specificity of these antibodies. First, culture surfaces coated with the antireceptor antibodies caused specific down modulation of C3bi receptor activity on M phi adherent to these substrates. Second, receptor protein purified by using IB4 or OKM1 retained the ability to bind selectively to C3bi-coated erythrocytes. Each of the antibodies recognizes a distinct epitope on the C3bi receptor; they do not compete with one another for binding to monocytes. Further, when immobilized on a solid support, each of the antibodies binds a molecule from M phi lysates that can simultaneously bind one of the other monoclonal anti-C3bi receptor antibodies. OKM10 binds and masks the ligand-binding site of the C3bi receptor, while IB4, OKM1, and OKM9 bind to sites remote from the C3bi binding site. All four antibodies immunoprecipitated polypeptides of Mr 185,000 and 105,000 from 125I-surface-labeled M phi. IB4 also precipitates polypeptides of Mr 185,000, 153,000, and 105,000. We conclude that the C3bi receptor of human M phi is a complex composed of two polypeptides, Mr 185,000 and 105,000. We have identified monoclonal antibodies reacting with four distinct antigenic determinants of this complex. The determinant recognized by antibody OKM10 is at or near the ligand-binding site of the receptor. The determinant recognized by antibody IB4 is shared by at least two other leukocyte surface proteins.

Five epitopes of a differentiation antigen on human inducer T cells distinguished by monoclonal antibodies

A series of mouse monoclonal antibodies reacting with human T cells of the helper/inducer subclass, OKT4, 4A, 4B, 4C, and 4D, have been reported. Using double-fluorescent staining and complement-mediated depletion, it was shown that the antigen(s) recognized by OKT4, 4A, 4B, 4C, and 4D antibodies are present on the same cell. Using FITC-labeled OKT4, 4A, 4B, 4C and 4D, a lack of competition between the antibodies for their epitopes was shown. Immunoprecipitation of the antigen recognized by each antibody yielded a molecule of approximately 60,000-62,000 Da. Sequential precipitation with several antibodies resulted in a minimum of additional precipitated antigen following removal of the first antigen. Capping of cell surface antigen with OKT4, followed by staining with OKT4, 4A, 4B, 4C, or 4D, indicated that the epitopes for all five antibodies co-cap. A sandwich ELISA assay using OKT4 and the other antibodies showed that molecules binding to OKT4A, 4B, 4C, and 4D also bound OKT4. It can therefore be concluded that monoclonal antibodies OKT4, 4A, 4B, 4C, and 4D recognize distinct epitopes present on a molecule of approximately 60-62,000 Da on human helper/inducer T cells.

Possible involvement of the T4 molecule in T cell recognition of class II HLA antigens: evidence from studies of proliferative responses to SB antigens

The T4 molecule has been identified as a marker of human T cell differentiation, but the function of this molecule remains to be defined. We have investigated its possible functional involvement in T cell proliferative responses to class II HLA antigens encoded by the recently described SB locus. The responses of SB-primed cells (specific for each of four different SB antigens) were studied with the use of two proliferation-inducing stimuli, SB antigen or TCGF. The proliferative responses to both stimuli were found to be mediated by T4+, T8- cells. Monoclonal antibodies against some epitopes on the T4 molecule (OKT4A and OKT4B) substantially blocked antigen-stimulated proliferative responses; antibodies against other epitopes of the T4 molecule (OKT4, T4C, T4D) blocked less well. Inhibition of SB-specific proliferation by antibodies to the T4 molecule was maximal only when the antibodies were incubated with the responder cells before the addition of stimulator cells. Proliferative responses of SB-primed cells stimulated with TCGF alone were not inhibited by any of the OKT4-related antibodies, but were completely inhibited by the anti-Tac monoclonal antibody, which reacts with the TCGF receptor. These results lend further support for the hypothesis that the T4 molecule is involved in T cell recognition of and/or activation by class II HLA antigens. We suggest that 1) the T4 molecule binds a nonpolymorphic epitope on class II HLA molecules, and 2) this interaction may facilitate, but not be an obligate requirement for, T cell activation by class II antigens.

Possible involvement of the T4 molecule in T cell recognition of class II HLA antigens: evidence from studies of proliferative responses to SB antigens

The T4 molecule has been identified as a marker of human T cell differentiation, but the function of this molecule remains to be defined. We have investigated its possible functional involvement in T cell proliferative responses to class II HLA antigens encoded by the recently described SB locus. The responses of SB-primed cells (specific for each of four different SB antigens) were studied with the use of two proliferation-inducing stimuli, SB antigen or TCGF. The proliferative responses to both stimuli were found to be mediated by T4+, T8- cells. Monoclonal antibodies against some epitopes on the T4 molecule (OKT4A and OKT4B) substantially blocked antigen-stimulated proliferative responses; antibodies against other epitopes of the T4 molecule (OKT4, T4C, T4D) blocked less well. Inhibition of SB-specific proliferation by antibodies to the T4 molecule was maximal only when the antibodies were incubated with the responder cells before the addition of stimulator cells. Proliferative responses of SB-primed cells stimulated with TCGF alone were not inhibited by any of the OKT4-related antibodies, but were completely inhibited by the anti-Tac monoclonal antibody, which reacts with the TCGF receptor. These results lend further support for the hypothesis that the T4 molecule is involved in T cell recognition of and/or activation by class II HLA antigens. We suggest that 1) the T4 molecule binds a nonpolymorphic epitope on class II HLA molecules, and 2) this interaction may facilitate, but not be an obligate requirement for, T cell activation by class II antigens.

Cell membrane perturbation of resting T cells and thymocytes causes display of activation antigens

Three human lymphocyte antigens recognized by monoclonal antibodies OKIa1, OKT9, and OKT10 were found to be minimally represented on resting peripheral T cells (all three) and thymocytes (OKIa1 and OKT9). These antigens, which are present on "activated" T cells, were promptly displayed on "resting" T cells or thymocytes following cross-linking of surface-bound monoclonal antibody by horse alpha-mouse IgG. These experiments suggested that membrane perturbations may induce the expression of certain antigens that are normally present in an unexpressed form in resting cells.

Patterns of antigenic expression on human monocytes as defined by monoclonal antibodies

A series of seven monoclonal antibodies directed at determinants on human peripheral blood monocytes were produced and characterized. The antibodies were separated into three groups based on cell distribution and percentages of monocytes bearing antigen. Hybridoma antibodies, termed OKM1, OKM9, and OKM10, recognized antigen(s) expressed on the majority of adherent monocytes, null cells, and granulocytes. The second group, comprising OKM5 and OKM8, reacted with most adherent monocytes and platelets. OKM3 and OKM6, comprising a third group of antibodies, reacted with a subpopulation of adherent monocytes and platelets. OKM antibodies were not expressed on lymphocytes, thymocytes, and lymphoblastoid cells, with the exception of OKM3 which reacted with three B-cell lines. SDS gels of immunoprecipitates formed with OKM antibodies yielded the following tentative molecular weight results: OKM1 and OKM9 antigens appeared to be 160,000 (nonreduced) and 170,000 (reduced); OKM10 precipitated two polypeptides of 170,000 and 115,000 (reduced); OKM5 and OKM8 precipitated a single polypeptide of 88,000 (reduced, nonreduced); OKM6 antigen appeared to be 116,000 (nonreduced) and 130,000 (reduced).

Functional subsets of human monocytes defined by monoclonal antibodies: a distinct subset of monocytes contains the cells capable of inducing the autologous mixed lymphocyte culture

The induction of most immune responses requires the close cooperation between T cells and antigen-presenting cells (APC), presumably of monocyte/macrophage (M phi) lineage. To characterize human APC further, we used two monoclonal antibodies, OKM1 and OKM5, to isolate and identify M phi subsets. OKM1 has been described and recognizes cell surface antigens on most M phi and granulocytes. OKM5 recognizes cell surface determinants present on the majority of human M phi but does not recognize other hematopoietic cell types. A small subset of peripheral blood M phi is OKM1-OKM5+. Human peripheral blood E- cells were separated into OKM1+ and OKM1- subsets by a rosetting technique utilizing anti-Ig-coated red cells. The capacity to present self antigens in the autologous mixed lymphocyte culture (AMLC) resided predominantly within the E-OKM1- subset, even if surface membrane Ig-positive cells were eliminated. Similar experiments showed that the ability to stimulate in AMLC was contained in the E-OKM5+ population and in fact resided primarily within the E-OKM1-OKM5+ subset. All of these subsets were able to trigger allogeneic T cells to proliferate. The capacity of these APC subsets to present soluble antigens (mumps, tetanus toxoid) was also examined. The data demonstrated that although the majority of these APC are E-OKM1+, E-OKM1-OKM5+ cells can also present foreign antigen. Taken together, these data suggest OKM1 and OKM5 can be used to isolate two functionally distinct human M phi subsets. One subset (E-OKM1+) is capable of presenting soluble antigens but shows minimal ability to trigger AMLC. The other subset (E-OKM1-OKM5+) can also present soluble antigens but is the predominant subset that can trigger AMLC.

Functional subsets of human monocytes defined by monoclonal antibodies: a distinct subset of monocytes contains the cells capable of inducing the autologous mixed lymphocyte culture

The induction of most immune responses requires the close cooperation between T cells and antigen-presenting cells (APC), presumably of monocyte/macrophage (M phi) lineage. To characterize human APC further, we used two monoclonal antibodies, OKM1 and OKM5, to isolate and identify M phi subsets. OKM1 has been described and recognizes cell surface antigens on most M phi and granulocytes. OKM5 recognizes cell surface determinants present on the majority of human M phi but does not recognize other hematopoietic cell types. A small subset of peripheral blood M phi is OKM1-OKM5+. Human peripheral blood E- cells were separated into OKM1+ and OKM1- subsets by a rosetting technique utilizing anti-Ig-coated red cells. The capacity to present self antigens in the autologous mixed lymphocyte culture (AMLC) resided predominantly within the E-OKM1- subset, even if surface membrane Ig-positive cells were eliminated. Similar experiments showed that the ability to stimulate in AMLC was contained in the E-OKM5+ population and in fact resided primarily within the E-OKM1-OKM5+ subset. All of these subsets were able to trigger allogeneic T cells to proliferate. The capacity of these APC subsets to present soluble antigens (mumps, tetanus toxoid) was also examined. The data demonstrated that although the majority of these APC are E-OKM1+, E-OKM1-OKM5+ cells can also present foreign antigen. Taken together, these data suggest OKM1 and OKM5 can be used to isolate two functionally distinct human M phi subsets. One subset (E-OKM1+) is capable of presenting soluble antigens but shows minimal ability to trigger AMLC. The other subset (E-OKM1-OKM5+) can also present soluble antigens but is the predominant subset that can trigger AMLC.

Resting and activation antigens of T cells: studies with OKT10 and OKT20 monoclonal antibodies

OKT10 and OKT20 are monoclonal antibodies that recognize cell surface antigen(s) on resting thymocytes, plasma cells, null cells, monocytes, and some bone marrow cells. The respective antigens, poorly expressed on resting peripheral T cells, are strongly expressed on T cells activated either in vitro or in vivo. Double-staining experiments using either OKT10 or OKT20, in combination with OKT3, provided paradoxical results. If indirect staining with OKT3 plus horse alpha-mouse IgG preceded staining with OKT10 or OKT20, most cells showed double staining; all other staining sequences yielded the expected result that OKT3+ cells expressed very little OKT10 or OKT20. Analysis of the experiments revealed that perturbation of the cell membrane with a monoclonal antibody reactive with a cell surface antigen (for example, OKT3) followed by a crosslinking second antibody caused the expression of these antigens. This suggests that these antigens, normally expressed on activated T cells, are actually present in an unexpressed form within the membrane of resting T cells.

Possible involvement of the OKT4 molecule in T cell recognition of class II HLA antigens. Evidence from studies of cytotoxic T lymphocytes specific for SB antigens

A recently described HLA gene, SB, which maps between GLO and HLA-DR, codes for Ia-like molecules that are similar to but distinct from HLA-DR molecules. Cytotoxic T lymphocytes (CTL) specific for SB1, SB2, SB3, and SB4 were compared with HLA-A2-specific CTL with respect to their surface expression of the T cell differentiation antigens OKT3, OKT4, and OKT8. All CTL activity was eliminated by treatment with OKT3 and C'. The SB-specific cytotoxicity was eliminated by OKT4 plus C' but not by OKT8 plus C'. In contrast, HLA-A2-specific killing was completely susceptible to treatment with OKT8 plus C' but not with OKT4 plus C'. Cytotoxicity was analyzed in the presence of OKT8 and a series of monoclonal antibodies (OKT4A, 4B, 4C, and 4D) that react with distinct epitopes on the OKT4 molecule. SB1-, SB3-, and SB4-specific CTL were partially inhibited by OKT4A and 4B (45-75%), whereas HLA-A2-specific CTL were partially inhibited by OKT8 (48-63%) but not by OKT4. SB2-specific CTL were not inhibited (less than 26%) by OKT8 or by any of the OKT4-related antibodies. These results suggest that the OKT4 marker may be expressed on most T cells that recognize allogeneic Ia or self Ia plus foreign antigens; OKT4+ cells do not appear to be functionally homogeneous in that they can act both as helper/inducer and cytotoxic cells. Models are proposed for the functional involvement of the OKT4 molecule in T cell-Ia antigen interactions.

Functional analysis of human T cell subsets defined by monoclonal antibodies. V. Suppressor cells within the activated OKT4+ population belong to a distinct subset

In the present report, we characterize a monoclonal antibody directed at a surface differentiation antigen on human T cells. The monoclonal antibody, OKT17, recognizes a cell surface antigen present on the majority of resting normal peripheral T cells. In contrast, OKT17 is unreactive with normal B cells, B cell lines, T cell lines, or SIg+ CLL. Interestingly, after activation, the antigen recognized by OKT17 is lost from a subset of OKT4+ cells. We took advantage of this finding to explore further the functional heterogeneity within activated OKT4+ cells. Evidence was obtained that the PWM-activated OKT4+ subset remaining after depletion of OKT17-reactive T cells (OKT4+ 17-) contains radiosensitive helperr cells but is devoid of suppressor cells. In contrast, the activated OKT4+ 17+ population contains potent radiosensitive suppressor cells as well as radioresistant helpe cells. Taken together, these studies suggest that the OKT17 monoclonal antibody can differentiate two functionally mature, activated OKT4+ human T cells: OKT4+ OKT17+ radiosensitive suppressor cells and OKT4+ 17- radiosensitive helper cells.

Functional analysis of human T cell subsets defined by monoclonal antibodies. V. Suppressor cells within the activated OKT4+ population belong to a distinct subset

In the present report, we characterize a monoclonal antibody directed at a surface differentiation antigen on human T cells. The monoclonal antibody, OKT17, recognizes a cell surface antigen present on the majority of resting normal peripheral T cells. In contrast, OKT17 is unreactive with normal B cells, B cell lines, T cell lines, or SIg+ CLL. Interestingly, after activation, the antigen recognized by OKT17 is lost from a subset of OKT4+ cells. We took advantage of this finding to explore further the functional heterogeneity within activated OKT4+ cells. Evidence was obtained that the PWM-activated OKT4+ subset remaining after depletion of OKT17-reactive T cells (OKT4+ 17-) contains radiosensitive helperr cells but is devoid of suppressor cells. In contrast, the activated OKT4+ 17+ population contains potent radiosensitive suppressor cells as well as radioresistant helpe cells. Taken together, these studies suggest that the OKT17 monoclonal antibody can differentiate two functionally mature, activated OKT4+ human T cells: OKT4+ OKT17+ radiosensitive suppressor cells and OKT4+ 17- radiosensitive helper cells.

Creating a useful panel of anti-T cell monoclonal antibodies

Monoclonal antibodies to human T lymphocyte surface markers were produced by cell fusions between splenocytes from mice, immunized with T lineage cells, and mouse myeloma cells. Our approaches to immunization, clone selection and analysis of the resultant monoclonal antibodies with similar reactivities were produced. In one example, we found that several distinct monoclonal antibodies identified the same T inducer subset yet, apparently, recognized epitopes of the differentiation antigen(s) on these cells.