Prevalence of coronary artery fistulae after cardiac surgery. Comparison between coronary artery bypass grafting, valve surgery, and orthotopic heart transplantation

INTRODUCTION

Coronary artery fistulae (CAF) are anomalous connections from a coronary artery to a recipient pulmonary vessel or cardiac chamber, and are reported in 0.2 % of the general population. The prevalence of CAF in the modern orthotopic heart transplant (OHT) population has been demonstrated to be significantly higher. The mechanism is unknown but one proposal is endothelial and vascular growth factor activation from injury. We hypothesize an incremental increase in CAF prevalence with the complexity of surgery, such that patients who have undergone OHT surgery would have an increased prevalence of CAF, as compared with patients who have undergone coronary artery bypass (CABG) surgery with valve surgery and as compared with patients who have undergone CABG surgery only.

PATIENTS AND METHODS

Consecutive angiograms of 481 patients after CABG surgery and 432 patients after OHT were reviewed. Patients who had previous valve surgery in addition to CABG were identified. Presence of CAF was determined. The chi-squared test was used for statistical analysis.

RESULTS

In all, 436 patients had CABG only (group A), 45 patients had CABG with valve surgery (group B), and 432 patients had OHT (group C). The mean age of patients at the time of surgery for group A, B, and C was 59.0, 66.1, and 55.3 years, respectively. The percentage of male patients was 78.4, 77.8, and 77.1 %, respectively. We found 10 patients (2.3 %) with CAF in group A compared with 4 patients (8.9 %) in group B, and 88 patients (20.4 %) in group C, which was statistically significant (p < 0.001). All CAF were small, were not associated with hemodynamic compromise or significant adverse events, and were managed conservatively.

CONCLUSION

There is an increased prevalence of CAF formation both after CABG and OHT compared with the general population. The higher prevalence of CAF in patients who additionally underwent valve surgery or who underwent OHT may be attributed to differences in surgical complexity. The increased prevalence of CAF formation after OHT compared with CABG should be further investigated.

Coronary artery to pulmonary artery fistulae with multiple aneurysms: radiological features on dual-source 64-slice CT angiography

Coronary artery fistula is a rare vascular anomaly in which there is abnormal communication between the coronary artery and the great vessels or cardiac chambers. We report the case of a 66-year-old man with two separate coronary artery to pulmonary artery fistulas (one of which demonstrated multiple aneurysms), which were diagnosed on dual-source 64-slice coronary CT and reconfirmed by coronary catheter angiography.

Current concepts in the diagnosis and management of metabolic complications of HIV infection and its therapy

Changes in fat distribution, dyslipidemia, disordered glucose metabolism, and lactic acidosis have emerged as significant challenges to the treatment of human immunodeficiency virus (HIV) infection. Over the past decade, numerous investigations have been conducted to better define these conditions, identify risk factors associated with their development, and test potential therapeutic interventions. The lack of standardized diagnostic criteria, as well as disparate study populations and research methods, have led to conflicting data regarding the diagnosis and treatment of metabolic and body shape disorders associated with HIV infection. On the basis of a review of the medical literature published and/or data presented before April 2006, we have prepared a guide to assist the clinician in the detection and management of these complications.

Meeting notes from the 2nd International AIDS Society Conference on HIV Pathogenesis and Treatment. Metabolic update: better defining lipodystrophy and treating insulin resistance

A large case-control study finds that lipoatrophy is the predominant fat abnormality in HIV-infected patients, and a small randomized, placebo-controlled study finds benefit for rosiglitazone for insulin resistance.

Comparative studies of two-times-daily versus three-times-daily indinavir in combination with zidovudine and lamivudine

OBJECTIVES

To compare the efficacy and safety of two-times-daily versus three-times-daily indinavir in combination with zidovudine and lamivudine.

DESIGN

Two multicenter, open-label, randomized 24-week studies.

METHODS

Adults HIV-1 infection, HIV-1 RNA greater than 10000 copies/ml, and no prior lamivudine or protease inhibitor therapy were eligible. In a pilot study (Study A), patients received indinavir at 800 mg every 8 h, 1000 mg every 12 h, or 1200 mg every 12 h. In a subsequent study (Study B), patients received indinavir at 800 mg every 8 h or 1200 mg every 12 h. All subjects received zidovudine (300 mg) and lamivudine (150 mg) every 12 h. An intent-to-treat analysis was used.

RESULTS

In Study A, which enrolled 88 patients, neither HIV-1 RNA nor CD4 cell responses differed significantly between treatment groups at 24 weeks when corrected for multiple comparisons. Study B enrolled 433 patients, but was prematurely discontinued when interim analysis suggested greater efficacy of three-times-daily indinavir. Of the first 87 patients reaching week 24, HIV-1 RNA was less than 400 copies/ml in 91% receiving three-times-daily versus 64% receiving two-times-daily indinavir (P < 0.01).

CONCLUSION

Three-times-daily indinavir appears more efficacious than two-times-daily dosing when administered with zidovudine and lamivudine. Two-times-daily indinavir dosing should only be considered in situations characterized by favorable pharmacokinetic drug-drug interactions.

High-risk behaviors during incarceration in African-American men treated for HIV at three Los Angeles public medical centers

OBJECTIVES

This paper describes research that examined the association between high-risk sexual and drug-using behaviors during incarceration and HIV infection for African-American men receiving HIV care at three public medical centers in Los Angeles County (LAC), California.

METHODS

A case-control study was conducted in which 305 HIV-infected African-American men and 305 neighborhood controls, ages 20 to 49, were frequency-matched by age.

RESULTS

After controlling for anal sex while not incarcerated, we found no association between anal sex during incarceration and HIV (odds ratio [OR], 1.1; 95% confidence interval [CI], 0.6-2.2). Among men with a history of incarceration (n = 332), the percentage reporting anal sex with men outside of incarceration (45%) was greater than those reporting anal sex while incarcerated (16%). Injection drug use (IDU) during incarceration was also not associated with HIV when controlling for IDU outside of incarceration (OR, 1.6; 95% CI, 0.5- 4.9). Increased time in jail or prison was associated with less HIV infection (p =.001).

CONCLUSIONS

Although high-risk behaviors are more common in the community than in the incarcerated setting for this study group, incarcerated populations represent a high-risk group for whom access to prevention messages is limited. Periods of incarceration represent a unique opportunity to convey prevention messages that focus on high-risk behaviors outside the incarcerated setting.

Effects of chronic heparin administration on coronary vascular adaptation to hypertension and ventricular hypertrophy in sheep

BACKGROUND

Hypertension decreases myocardial perfusion capacity in adults for several reasons, including insufficient coronary angiogenesis with left ventricular (LV) hypertrophy, arteriolar hypertrophy, and altered vasomotion. Heparin influences growth factors that promote angiogenesis and vasodilation and inhibit arteriolar wall thickening.

METHODS AND RESULTS

Adult sheep were given heparin 200 U/kg body wt SC twice daily throughout 6 weeks of LV and coronary hypertension from a progressively constricted ascending aortic band (n=14). They were compared with untreated sheep with (n=13) and without (n=13) aortic stenosis. After 6 weeks, maximum myocardial perfusion was measured during adenosine infusion in the conscious state by the microsphere method. Sheep with aortic stenosis had less maximum coronary flow per gram, less conductance reserve, and thicker arteriolar walls in the LV and nonhypertrophied right ventricle. Capillary density decreased in the LV endomyocardium and remained unchanged in the right ventricle. Heparin-treated sheep had significant partial normalization of coronary conductance reserve and maximum perfusion in both ventricles and capillary density in the LV endomyocardium. Arteriolar wall thickness was unchanged. Compared with untreated sheep with aortic stenosis, in heparin-treated sheep LV FGF-2 protein increased 2-fold, whereas FGF-2 mRNA remained unchanged. VEGF mRNA and protein increased 3-fold and 1.4-fold, respectively, whereas TGF-beta(1) mRNA declined 3-fold.

CONCLUSIONS

Heparin administration during LV hypertension increases heparin-binding angiogenic factors FGF-2 and VEGF in the LV and ameliorates decreases in LV perfusion capacity and capillary density.

Invariant or highly conserved TCR alpha are expressed on double-negative (CD3+CD4-CD8-) and CD8+ T cells

TCR alpha (TCRA) expression was examined in RNA samples from PBMC and isolated populations of CD4+, CD8+, and DN T cells from 15 healthy individuals. The expressed TCR repertoire was surveyed using spectratype analysis, a technique that displays the distribution of complementarity determining region 3 (CDR3) lengths for each TCRAV gene family. The results revealed the presence of unusual populations of double-negative (DN; CD4-CD8-CD3+) T cells that express invariant or conserved TCRAV4A, AV7, AV19, and AV24 chains. Each of the conserved TCRA families was over-represented in >70% of the individuals studied, and all individuals expressed at least one of the over-represented TCRAV families. Over-represented conserved AV4A or AV7 sequences were also present in CD8+ T cells from most donors. The extent of TCRA sequence conservation is unparalleled. TCRAV4A, AV19, and AV24 sequences were invariant, although AV4A and AV19 transcripts contained N region additions. TCRAV24 transcripts derived from the direct juxtaposition of V and J gene segments. TCRAV7 sequences showed some diversity in two amino acids encoded at junctions of V and J gene segments. Although derivation of DN T cells with conserved TCRA chains is puzzling, the wide-spread expression of these unusual cells suggests an important function.

A phase II/III trial of antimicrobial therapy with or without amikacin in the treatment of disseminated Mycobacterium avium infection in HIV-infected individuals. AIDS Clinical Trials Group Protocol 135 Study Team

OBJECTIVE

To determine the clinical and microbiologic benefit of adding amikacin to a four-drug oral regimen for treatment of disseminated Mycobacterium avium infection in HIV-infected patients.

DESIGN

A randomized, open-labeled, comparative trial.

SETTING

Outpatient clinics.

PATIENTS

Seventy-four patients with HIV and symptomatic bacteremic M. avium infection.

INTERVENTIONS

Rifampin 10 mg/kg daily, ciprofloxacin 500 mg twice daily, clofazimine 100 mg every day, and ethambutol 15 mg/kg orally daily for 24 weeks, with or without amikacin 10 mg/kg intravenously or intramuscularly 5 days weekly for the first 4 weeks.

MAIN OUTCOME MEASURE

Clinical and microbiologic response at 4 weeks; quantitative level of bacteremia with M. avium.

RESULTS

No difference in clinical response was noted with the addition of amikacin to the four-drug oral regimen, and only 25% in either group had a complete or partial response at 4 weeks. A comparable quantitative decrease in bacteremia was noted in both treatment groups, with 16% of patients being culture-negative at 4 weeks and 38% at 12 weeks. Toxicities were mainly gastrointestinal. Amikacin was well tolerated. Median survival was 30 weeks in both groups.

CONCLUSIONS

The addition of amikacin to a four-drug oral regimen of rifampin, ciprofloxacin, clofazimine, and ethambutol did not provide clinical or microbiologic benefit.

Comparison of the sheath delivery system versus bare stenting for coronary stent implantation

Outside the United States, Palmaz-Schatz coronary stents are implanted by hand-crimping the stent to a high pressure balloon without the use of a protective sheath. This lowers the delivery profile, increases the ease of deployment, and ensures that the postdilatation balloon is centered on the stent. To assess this bare stenting technique, 209 patients were retrospectively analyzed: 92 patients (107 lesions) with the sheath protected stent delivery system (SDS) and 117 patients (150 lesions) with the bare stent approach. The number of balloons used per lesion in the bare stent group was significantly less than in the SDS group (1.9 +/- 0.6 vs. 3.8 +/- 1.2, P < 0.0001). In addition, the procedure time in the bare stent group was significantly shorter than in the SDS group (106 +/- 55 vs. 134 +/- 60 min, P = 0.001). There was no difference in frequency of adverse events or stent displacement during the procedure. The bare stenting technique decreases the procedure time, reduces the number of balloons used, and is as safe as the SDS approach.

Human immunodeficiency virus replication in AIDS patients with Mycobacterium avium complex bacteremia: a case control study. California Collaborative Treatment Group

The development of opportunistic infections and the administration of vaccines have been associated with transient increases of human immunodeficiency virus (HIV) RNA plasma levels in HIV-infected patients. To determine the relationship between Mycobacterium avium complex (MAC) bacteremia and HIV RNA levels, HIV RNA levels in patients who developed MAC bacteremia (cases) were compared with levels in patients who remained free of MAC disease (controls). Cases and controls were matched for CD4 cell count, prophylaxis against MAC disease, antiretroviral therapy, and duration of follow-up. Mean baseline HIV RNA levels were 4.8 log10 copies/mL in cases and 4.6 log10 copies/mL in controls (P = 0.22). HIV RNA levels increased by a median of 0.4 log in cases but not controls at the time of MAC bacteremia (P = 0.01). In AIDS patients, the onset of MAC bacteremia is associated with a modest but significant increase in serum HIV RNA levels. Increased HIV replication may contribute to the higher mortality associated with MAC bacteremia.

Remodeling of the coronary artery after vascular injury

Vascular injury, such as angioplasty, induces a complex healing process that is analogous to generalized wound healing. Following initial injury, platelet thrombi and an acute inflammatory response occur, followed by cellular inhibition by monocytes/macrophages, proliferation of vascular smooth muscle cells, and extracellular matrix deposition. The injury repair concludes with organization of the matrix and reendothelialization. Recent studies suggest that restenosis or renarrowing after vascular injury is due to two components: a cellular proliferative process leading to intimal hyperplasia and remodeling of the vessel with a change in vessel geometry. Animal and clinical studies have shown that at least 60% of restenosis can be explained by unfavorable remodeling with vessel constriction rather than intimal hyperplasia. Although a number of factors appear to be associated with remodeling, alterations in extracellular matrix metabolism may be most important.

Women and HIV. A review of current epidemiology, gynecologic manifestations, and perinatal transmission

HIV is increasing rapidly in women, particularly due to heterosexual transmission. The manifestations of HIV in women differ in some respects from those in men, most obviously with respect to gynecologic manifestations. Candidiasis, anogenital human papillomavirus and neoplasia, and contraception and prevention of sexual transmission are all important issues. Reduction in perinatal transmission is a key focus in women, with a growing number of effective preventative interventions.

Guidelines for management of HIV infection with computer-based patient's record

Computers are steadily being incorporated in clinical practice. We conducted a nonrandomised, controlled, prospective trial of electronic messages designed to enhance adherence to clinical practice guidelines. We studied 126 physicians and nurse practitioners who used electronic medical records when caring for 349 patients with HIV infection in a primary care practice. We analysed the response times of clinicians to the situations that triggered alerts and reminders, the number of ambulatory visits, and hospitalisation. The median response times to 303 alerts in the intervention group and 388 alerts in the control group were 11 and 52 days (p < 0.0001), respectively. The median response time to 432 reminders in the intervention group was 114 days and that for 360 reminders in the control group was over 500 days (p < 0.0001). There was no effect on visits to the primary care practice. There was, however, a significant increase in the rate of visits outside the primary care practice (p = 0.02), which is explained by the increased frequency of visits to ophthalmologists. There were no differences in admission rates (p = 0.47), in admissions for pneumocystosis (p = 0.09), in visits to the emergency ward (p = 0.24), or in survival (p = 0.19). We conclude that the electronic medical record was effective in helping clinicians adhere to practice guidelines.

Antigens released at schizont burst stimulate Plasmodium falciparum-specific CD4+ T cells from non-exposed donors: potential for cross-reactive memory T cells to cause disease

In an individual experiencing the first attack of malaria, symptoms of disease can occur at very low parasitemia. T cells and cytokines have been implicated in the etiology of disease symptoms, and others and ourselves have shown that T cells from non-exposed individuals can be stimulated by malaria parasites. Here, we show that nine from 11 blood samples, naturally infected with malaria parasites, could stimulate proliferation of a malaria-specific T cell clone derived from a non-exposed donor. T cells were able to respond to infected blood at a parasitaemia as low as 0.000003% (comparable to the level at which individuals can first experience symptoms of malaria) and secrete cytokines implicated in pathology. Antigens capable of stimulating T cells are expressed throughout the blood stage, but are specifically released at the time of schizont rupture. While most TCR V beta genes are expressed during the T cell response of naive donors to malaria parasites, processing of parasite antigens is blocked by chloroquine and monensin, and activation of 36 of 41 malaria-specific clones tested was restricted by defined MHC class II allelic antigens, strongly suggesting that parasites do not act as mitogens nor as superantigens. The clones react to various commonly encountered pathogenic and non-pathogenic microbes. These data support the concept that activation of cross-reactive memory T cells by malaria parasites contributes to disease symptoms in individuals experiencing their first attack of malaria.

Inhibition of Plasmodium falciparum growth in vitro by CD4+ and CD8+ T cells from non-exposed donors

T cells from most adult non-exposed donors, which express a memory phenotype (CD45RO+), can respond by proliferation to P. falciparum asexual stages in vitro. Such cells may have arisen from exposure to environmental organisms. To address the efficacy of such cells in eliminating parasites and investigate the mechanisms involved, we have used an in vitro assay where parasite growth can be precisely monitored in the presence of different cell preparations. Unfractionated peripheral blood mononuclear cells (PBMC) from both malaria-exposed and non-exposed donors inhibited parasite growth by up to 62% in a two day assay. Purified T cells in the presence of adherent cells had a similar effect, but purified T cells alone or adherent cells alone had minimal effect. Antigens released at the time of schizont rupture were maximally effective in stimulating interferon-gamma (IFN gamma) production. Neutralizing antibodies to IFN gamma showed a partial reduction of growth inhibition in some individuals tested suggesting that different mechanisms may be operative. Neutralizing antibody to TNF alpha had a partial effect in combination with anti-IFN gamma. Antibodies to IL-1 and IL-4 had no effect. T cell fractionation experiments showed that while purified CD4+ T cells from some donors produced IFN gamma and inhibited parasite growth, purified CD8+ T cells could inhibit parasite growth to a greater extent without production of detectable IFN gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of human T cell clones specific for conserved peptide sequences within malaria proteins. Paucity of clones responsive to intact parasites

T cells are thought to be of central importance in malaria immunity. Peptides copying malaria protein sequences often stimulate human CD4+ T cells and it was thought that they represented T cell epitopes present in the parasite and may thus have particular relevance to malaria vaccine development. To verify whether synthetic peptides representing highly conserved regions of parasite Ags may contribute to a malaria vaccine, we searched the data bank for conserved regions of Plasmodium falciparum malaria proteins that were not homologous to known self (human) proteins. We synthesized 24 such peptides representing 11 of the cloned and sequenced malaria asexual stage Ags, which were predicted by algorithms to represent T cell epitopes, and 6 peptides not predicted to be T cell epitopes and used these to generate T cell clones from individuals with an extensive previous history of malaria exposure. The T cell clones responded vigorously to many peptides but only a single clone, specific for a peptide within merozoite surface protein-1, 20-39, VTHESYQELVKKLEALEDAV, and not previously defined to be a T cell epitope responded to malaria parasites by proliferation and secretion of IFN-gamma. This epitope was not revealed by studying parasite-induced T cell lines and is thus subdominant. The clone was able to significantly inhibit parasite growth in vitro. The final step in the inhibition of parasite growth appears to be nonspecific because other activated clones (not specific for malaria sequences) can inhibit parasite growth. Our data suggest that few conserved peptides within malaria parasites can be processed from the intact parasite. However, such peptides that can be processed from malaria parasites may be expected to stimulate parasite-specific T cells that could inhibit parasite growth and as such may be lead candidates for a vaccine aimed at inducing cellular immunity to malaria.

Analysis of human T cell clones specific for conserved peptide sequences within malaria proteins. Paucity of clones responsive to intact parasites

T cells are thought to be of central importance in malaria immunity. Peptides copying malaria protein sequences often stimulate human CD4+ T cells and it was thought that they represented T cell epitopes present in the parasite and may thus have particular relevance to malaria vaccine development. To verify whether synthetic peptides representing highly conserved regions of parasite Ags may contribute to a malaria vaccine, we searched the data bank for conserved regions of Plasmodium falciparum malaria proteins that were not homologous to known self (human) proteins. We synthesized 24 such peptides representing 11 of the cloned and sequenced malaria asexual stage Ags, which were predicted by algorithms to represent T cell epitopes, and 6 peptides not predicted to be T cell epitopes and used these to generate T cell clones from individuals with an extensive previous history of malaria exposure. The T cell clones responded vigorously to many peptides but only a single clone, specific for a peptide within merozoite surface protein-1, 20-39, VTHESYQELVKKLEALEDAV, and not previously defined to be a T cell epitope responded to malaria parasites by proliferation and secretion of IFN-gamma. This epitope was not revealed by studying parasite-induced T cell lines and is thus subdominant. The clone was able to significantly inhibit parasite growth in vitro. The final step in the inhibition of parasite growth appears to be nonspecific because other activated clones (not specific for malaria sequences) can inhibit parasite growth. Our data suggest that few conserved peptides within malaria parasites can be processed from the intact parasite. However, such peptides that can be processed from malaria parasites may be expected to stimulate parasite-specific T cells that could inhibit parasite growth and as such may be lead candidates for a vaccine aimed at inducing cellular immunity to malaria.

'Original antigenic sin', T cell memory, and malaria sporozoite immunity: an hypothesis for immune evasion

Prior to any exposure to malaria, most adults have T cells specific for malaria parasites and various malaria proteins. The protein for which this has been shown more than any other is the circumsporozoite protein (CSP) of Plasmodium falciparum. These T cells can be present in high frequency and appear to have arisen through exposure to other (non-malaria) organisms. Although T cells are thought to provide protection against sporozoites, these T cells specific for cross-reactive organisms are clearly unable to protect against malaria, and may be preferentially expanded following exposure to malaria sporozoites. Thus, cross-reactive organisms have the potential to skew the repertoire of sporozoite-induced T cells and affect the induction of protective immunity. This is analogous to the concept of 'original antigenic sin' whereby prior exposure to one strain of influenza virus was shown to be able to divert the antibody response to a second challenging strain to focus on the shared (cross-reactive) epitopes.

An electronic medical record that helps care for patients with HIV infection

We have built a clinical workstation to help doctors and nurses care for patients with HIV infection. This knowledge-based medical record system provides medication alerts, reminders about primary care, and on-line information to support the care of patients with HIV infection. We are conducting a controlled clinical trial of this computer system in a single practice setting, which consists of 18 staff physicians, 13 nurses, and 113 residents, who cooperatively practice in four teams. Two teams of physicians are assigned to an intervention group and two teams to a control group. This paper reports preliminary results from the first year of study, January 15, 1992, through January 14, 1993. During this period 274 patients with HIV infection were followed by the general medical practice--130 in a control group and 144 in an intervention group. Physicians in the intervention group more rapidly and more completely followed primary care guidelines than did physicians in the control group. Patients in the intervention group had 2476 ambulatory or emergency visits (17.2 visits per patient) compared with 1882 visits (14.5 visits per patient) for the control patients (p < 0.01). There were 101 hospitalizations for 51 patients in the intervention group (an admission rate of 0.7) compared with 104 admissions for 54 patients in the control group (an admission rate of 0.8) (p = NS). There were 8 deaths in the intervention group (5.6%) compared with 13 (10%) in the control group (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

The importance of T cell homing and the spleen in reaching a balance between malaria immunity and immunopathology: the moulding of immunity by early exposure to cross-reactive organisms

It takes a number of years to develop clinical immunity to malaria and malaria pathology is also most evident a number of years after birth. T cells are known to play an important role in defence from malaria parasites but may also contribute to the disease symptoms associated with malaria. T cells which react against malaria parasites have arisen through stimulation with organisms which cross-react with malaria or through exposure to the malaria parasites themselves and express a memory phenotype (CD45Ro+, CD45Ra-, CD4+). T clones which have arisen through exposure to cross-reactive organisms may be expected to home to the tissues where initial exposure occurred as determined by tissue-specific adhesion molecules on the lymphocyte surface. Such tissues may not be appropriate to parasite killing and localization of T cells in such sites may contribute to the immunopathology of malaria. The sharp increase in immunity and decline in pathology observed in later childhood in malaria endemic areas may result from an increase in the number of T cells induced by the parasite itself (as opposed to cross-reactive organisms). Such T cells may not have a preferential trafficking to other organs and may be more likely to circulate through the spleen. Splenic changes may also allow more malaria-specific T cells to concentrate in the spleen and may facilitate interactions between T cells, monocytes, neutrophils and parasites resulting in parasite death. Whereas cytokines secreted by parasite-reactive T cells in all locations may contribute to cerebral malaria and other forms of pathology, cytokines in the spleen at least, should directly contribute to parasite death.

'Natural' T cells responsive to malaria: evidence implicating immunological cross-reactivity in the maintenance of TCR alpha beta+ malaria-specific responses from non-exposed donors

It is now generally accepted that peripheral blood of humans not exposed previously to malaria contains T cells which proliferate vigorously in response to malaria parasites and antigens. Although it has been claimed that these cells express a memory phenotype, their origin is uncertain. We have examined the phenotype and immunological responses of such cells. We confirm that these cells do express the 'memory phenotype', CD45Ro, in that depletion of such cells, but not of CD45Ra (virgin) cells, abrogates the immune response to malaria parasites. In an effort to define the genesis of these responses, numerous malaria-specific T cell clones have been generated from non-exposed individuals. These were tested for reactivity to a large panel of common bacterial, viral, and fungal pathogenic and non-pathogenic organisms. Most clones proliferated vigorously in response to one or more such organisms, while many clones demonstrated smaller but significant degrees of proliferation in response to many different organisms. Our data offers insights into the maintenance of immunological memory. All clones examined were CD3+, CD4+, CD8-, TCR alpha beta+, and TCR delta-. The ratio of TCR alpha beta+ to TCR delta+ cells among peripheral blood lymphocytes increased during polyclonal culture in the presence of parasite. The high frequency of such cells in peripheral blood (1/800-1/9000), and their response to a wide range of geographically different Plasmodium falciparum isolates and clones by both proliferation and lymphokine secretion (predominantly IFN-gamma) with a high degree of sensitivity (less than 1 parasite/microliters blood in some cases) suggests that these cells must be quickly activated following malaria infection. Their contribution to the outcome of the disease (protection/immunopathology) may be significant.

High frequency of malaria-specific T cells in non-exposed humans

A major goal of current candidate malaria vaccines is to stimulate the expansion of clones of malaria-specific lymphocytes. We have examined the in vitro T cell responses of a group of malaria exposed and non-exposed adult Caucasian donors to recombinant circumsporozoite (CS) proteins, one of which is undergoing clinical trials, to blood-stage parasites, and to synthetic peptides copying the CS protein and defined blood-stage proteins. In nearly all individuals tested, CD4 T cell proliferation or lymphokine production occurred in response to whole parasite or CS protein stimulation, and T cells from many individuals responded to synthetic peptides. T cell responses were major histocompatibility complex-restricted, and stimulation of T cells with malaria parasites or CS protein did not appear to expand a population of T cell receptor gamma/delta cells. Malaria-specific responses were independent of prior malaria exposure, and in some cases exceeded the magnitude of response to tetanus toxoid. Specific T cells are present in high frequency in the peripheral blood of many donors who have never been exposed to malaria. Although malaria-specific CD4 T cells play an important role in immunity, these data question whether vaccines need to stimulate such cells, and focus attention on other aspects of malaria immunity which may be more critical to a successful vaccine.

Monoclonal antibodies that bind to the My23 human myeloid cell surface molecule: epitope analysis and antigen modulation studies

It has previously been shown that the AML-2-23 monoclonal antibody (MoAb) reacts with a glycoprotein on differentiated myeloid cells. The antigen, My23, is released from these cells in culture and is also detectable in normal human plasma. We have now raised a panel of MoAbs against the soluble form of the antigen which reacts with monocytes and calcitriol-treated U937 and HL-60 myeloid cell lines, but not with lymphocytes or undifferentiated U937 and HL-60 cells. As with the AML-2-23 MoAb, the anti-My23 MoAbs immunoprecipitated a 50,000-55,000 protein from calcitriol treated HL-60 cells. Besides binding to cell surface My23, all eight MoAbs as well as the 63D3 MoAb reacted with crude and purified forms of soluble My23. A novel ELISA epitope analysis assay was developed to identify four distinct antigenic determinants on My23. Thus, the soluble and cell surface forms of My23 share several antigenic determinants and are biochemically very similar. Pooled anti-My23 caused selective patching, capping and clearing of My23 from the cell surface. My23 was not associated with cell surface, HLA-DR, HLA-A,B,C, beta 2-microglobulin or the Fc receptors for IgG or IgA. These anti-My23 MoAbs should be of importance in antigen functional studies and in clinical treatment protocols for patients with acute myelogenous leukemia. Furthermore, we have shown that a soluble myeloid differentiation antigen can serve as an effective immunogen for the preparation of MoAbs against important cell surface molecules thus obviating many problems inherent in the use of whole cells or detergent lysate-derived immunoprecipitates as immunogens.