A ferritin-based COVID-19 nanoparticle vaccine that elicits robust, durable, broad-spectrum neutralizing antisera in non-human primates

While the rapid development of COVID-19 vaccines has been a scientific triumph, the need remains for a globally available vaccine that provides longer-lasting immunity against present and future SARS-CoV-2 variants of concern (VOCs). Here, we describe DCFHP, a ferritin-based, protein-nanoparticle vaccine candidate that, when formulated with aluminum hydroxide as the sole adjuvant (DCFHP-alum), elicits potent and durable neutralizing antisera in non-human primates against known VOCs, including Omicron BQ.1, as well as against SARS-CoV-1. Following a booster ~one year after the initial immunization, DCFHP-alum elicits a robust anamnestic response. To enable global accessibility, we generated a cell line that can enable production of thousands of vaccine doses per liter of cell culture and show that DCFHP-alum maintains potency for at least 14 days at temperatures exceeding standard room temperature. DCFHP-alum has potential as a once-yearly (or less frequent) booster vaccine, and as a primary vaccine for pediatric use including in infants.

A ferritin-based COVID-19 nanoparticle vaccine that elicits robust, durable, broad-spectrum neutralizing antisera in non-human primates

While the rapid development of COVID-19 vaccines has been a scientific triumph, the need remains for a globally available vaccine that provides longer-lasting immunity against present and future SARS-CoV-2 variants of concern (VOCs). Here, we describe DCFHP, a ferritin-based, protein-nanoparticle vaccine candidate that, when formulated with aluminum hydroxide as the sole adjuvant (DCFHP-alum), elicits potent and durable neutralizing antisera in non-human primates against known VOCs, including Omicron BQ.1, as well as against SARS-CoV-1. Following a booster ∼one year after the initial immunization, DCFHP-alum elicits a robust anamnestic response. To enable global accessibility, we generated a cell line that can enable production of thousands of vaccine doses per liter of cell culture and show that DCFHP-alum maintains potency for at least 14 days at temperatures exceeding standard room temperature. DCFHP-alum has potential as a once-yearly booster vaccine, and as a primary vaccine for pediatric use including in infants.

MGNREGA in the Times of COVID-19 and Beyond: Can India do More with Less?

Covid-19 has ushered in a renewed focus on health, sanitisation and, in unexpected ways, on the need for productive employment opportunities in rural India. MGNREGA, the rural employment guarantee programme, has had a mixed track record in terms of providing adequate employment to those who need it the most, the quality of asset creation and adequacy of wages offered. This paper makes a case for reorienting a small portion of MGNREGA spending to create micro-entrepreneurs out of the 'reverse migrating' masons, electricians, plumbers and others in rural areas who can directly contribute to augmenting health and sanitization infrastructure in the likely new normal. This will provide relief to those whose livelihoods have been severely impacted and eventually lower dependence on public finances. We propose approval of a new work type for sanitization works without any hard asset creation under MGNREGA and roping in the private sector for its project management skills to quickly skill up the returning migrants as well as to match work with workers on an ongoing basis.

Infectious dose-dependent accumulation of live highly pathogenic avian influenza H5N1 virus in chicken skeletal muscle-implications for public health

Highly pathogenic avian influenza viruses (HPAIV) of H5N1 subtype are a major global threat to poultry and public health. Export of poultry products, such as chicken and duck meat, is a known source for the cross-boundary spread of HPAI H5N1 viruses. Humans get infected with HPAI H5N1 viruses either by close contact with infected poultry or through consumption of fresh/undercooked poultry meat. Skeletal muscle is the largest soft tissue in chicken that has been shown to contain virus during systemic HPAIV infection and supports productive virus infection. However, the time between infection of a chicken with H5N1 virus and presence of virus in muscle tissue is not yet known. Further, it is also not clear whether chicken infected with low doses of H5N1 virus that cause non-fatal subclinical infections continue to accumulate virus in skeletal muscle. We investigated the amount and duration of virus detection in skeletal muscle of chicken experimentally infected with different doses (10² , 10³ and 10⁴ EID₅₀ ) of a HPAI H5N1 virus. Influenza viral antigen could be detected as early as 6 hr after infection and live virus was recovered from 48 hr after infection. Notably, chicken infected with lower levels of HPAI H5N1 virus (i.e., 10² EID₅₀ ) did not die acutely, but continued to accumulate high levels of H5N1 virus in skeletal muscle until 6 days post-infection. Our data suggest that there is a potential risk of human exposure to H5N1 virus through meat from clinically healthy chicken infected with a low dose of virus. Our results highlight the need to implement rigorous monitoring systems to screen poultry meat from H5N1 endemic countries to limit the global spread of H5N1 viruses.

Temperature dependent soret spectral band shifts accompany human CN-mesohemoglobin assembly

The interaction between human apohemoglobin A and CN-Mesohemin, a monomeric non-native heme derivative, was probed by Soret spectrophotometric titrations in 0.05 M potassium phosphate buffer, pH 7 at varied temperatures. Hypsochromic shifts in the absorbance maxima were observed at all temperatures below 10 degrees C. First derivative spectroscopy of CN-Mesohemin titrations was used to provide further evidence of a spectral shift upon CN-Mesohemoglobin assembly. Findings of Soret Spectral shifts demonstrate a preference for the alpha chain heme site by CN-Mesohemin indicative of semi-alpha-hemoglobin intermediate formation. CN-Mesohemin, a derivative with peripheral 2,4 ethyl groups, does not possess the extended conjugation seen for native CN-Protohemin with its 2,4 vinyl groups. Indeed, reduced polarity of CN-Mesohemin over that of CN-Protohemin resulted in distinct temperature dependencies. Molecular visualization and protein-ligand interaction analysis targeted a functionally diverse residue unique to the alpha-chain. Tyrosine-42 (a polar/non-polar amino acid) appeared to play a prominent role in the assembly process.

Soret Spectral and Bioinformatic Approaches Provide Evidence for a Critical Role of the α -Subunit in Assembly of Tetrameric Hemoglobin

Soret spectral contributions of the alpha-subunit heme pocket have been evaluated by performing static titrations of apohemoglobin A with CNProtohemin under varied experimental conditions. Increasing the temperature from 5 to 30 degrees C in 0.05 M potassium phosphate buffer, pH 7, resulted in a decreasingly prominent hypsochromic shifts reflecting altered the vinyl-globin interactions. Studies at 10 degrees C in over pH range of 6.7-8.0 revealed a profile for the spectral shifts approximating the side chain pK value (7.4) a histidyl residue. These overall spectral changes correspond to DeltaE of < or = 7 kJ/mol indicative of electrostatic noncovalent interactions. Further our current molecular modeling studies indicate that the spatial arrangement and critical noncovalent interactions of tyrosine 42 and histidine 45 (aromatic residues unique to the alpha-subunit) make significant contribution to the Soret spectra. Most interestingly, phylogenetic analyses have revealed the presence of a histidyl triad in the alpha-chain of all vertebrates that form heterotetramers.

Ordered heme binding ensures the assembly of fully functional hemoglobin: a hypothesis

The exact mechanism by which four Fe-Protoporphyrin-IX (heme) moieties and four nascent globin chains combine to form human hemoglobin (alpha(2)beta(2)) remains a mystery. Recent Soret spectral static and kinetic studies of the incorporation of CN-Hemin derivatives into an array of human globin species have provided in vitro evidence of an ordered assembly pathway, through an alphaheme-betaglobin intermediate, that ensures correct formation of active hemoglobin tetramers.

Consequence of beta 16 and beta 112 replacements on the kinetics of hemoglobin assembly

The rates of alpha/beta monomer combination of four beta(A) variants (beta 112C --> S, beta 112C --> D, beta 112C --> T, and beta 112C --> V) in the presence and absence of beta 16G --> D (beta(J)) were measured in an attempt to assess the consequences of amino acid substitution at both a surface (beta 16) and an alpha(1)beta(1) interface (beta 112) residue on oxyhemoglobin assembly. Rates of alpha/beta monomer combination determined spectrally in 0.1 M Tris-HCl, 0.1 M NaCl, 1 mM EDTA, pH 7.4, at 21.5 degrees C differed by over 40-fold (22 +/- 2.0 to 0.49 +/- 0.1 x 10(5) M(-1) s(-1)), and were in the order: HbA beta 112S = HbJ beta 16D, beta 112S > HbA beta 112D = HbJ beta 16D, beta 112D > HbA > Hb J > HbA beta 112T = HbJ beta 16D, beta 112T > HbJ beta 16D, beta 112V > HbA beta 112V. This extensive kinetic investigation of single/double amino acid-substituted recombinant hemoglobin molecules, in conjunction with molecular modeling studies, has allowed examination of an array of unique alpha/beta subunit interactions and assembly processes.

Point mutations in a nucleoside transporter gene from Leishmania donovani confer drug resistance and alter substrate selectivity

Leishmania parasites lack a purine biosynthetic pathway and depend on surface nucleoside and nucleobase transporters to provide them with host purines. Leishmania donovani possess two closely related genes that encode high affinity adenosine-pyrimidine nucleoside transporters LdNT1.1 and LdNT1.2 and that transport the toxic adenosine analog tubercidin in addition to the natural substrates. In this study, we have characterized a drug-resistant clonal mutant of L. donovani (TUBA5) that is deficient in LdNT1 transport and consequently resistant to tubercidin. In TUBA5 cells, the LdNT1.2 genes had the same sequence as wild-type cells. However, because LdNT1.2 mRNA is not detectable in either wild-type or TUBA5 promastigotes, LdNT1.2 does not contribute to nucleoside transport in this stage of the life cycle. In contrast, the TUBA5 cells were compound heterozygotes at the LdNT1.1 locus containing two mutant alleles that encompassed distinct point mutations, each of which impaired transport function. One of the mutant LdNT1.1 alleles encoded a G183D substitution in predicted TM 5, and the other allele contained a C337Y change in predicted TM 7. Whereas G183D and C337Y mutants had only slightly elevated adenosine K(m) values, the severe impairment in transport resulted from drastically ( approximately 20-fold) reduced V(max) values. Because these transporters were correctly targeted to the plasma membrane, the reduction in V(max) apparently resulted from a defect in translocation. Strikingly, G183 was essential for pyrimidine nucleoside but not adenosine transport. A mutant transporter with a G183A substitution had an altered substrate specificity, exhibiting robust adenosine transport but undetectable uridine uptake. These results suggest that TM 5 is likely to form part of the nucleoside translocation pathway in LdNT1.1

Wavelength-dependent spectral changes accompany CN-hemin binding to human apohemoglobin

The interaction of apohemoglobin with two heme derivatives, CN-protohemin and CN-deutero-hemin, was monitored at multiple Soret wavelengths (417-423 and 406-412 nm, respectively) in 0.05 M potassium phosphate buffer, pH 7.0, at 10 degrees C and revealed, as previously reported, a multiphasic kinetic reaction. Wavelength-dependent reactions were observed for both CN-protohemin and CN-deuterohemin derivatives with the alpha chain (bathochromic entity) displaying faster (4- to 7-fold) rates throughout the courses of both heme-binding reactions. The basis of this spectrally heterogeneous kinetic phenomenon could be deduced from molecular modeling studies of alpha- and beta-chain structures. Key differences in the number of stabilizing contacts of the two chains with the peripheral alpha propionyl 45(CE3); 58(E7); 61(E10) as well as the beta vinyl 38(C4); 71(E15); 106(G8) groups were found. Furthermore, RMS plots comparing apo- and heme-containing subunits reveal substantial structural disparities in the C-CD-F-FG helical regions of the alphabeta dimer interface.

Cloning of a novel inosine-guanosine transporter gene from Leishmania donovani by functional rescue of a transport-deficient mutant

Purine transport is an indispensable nutritional function for protozoan parasites, since they are incapable of purine biosynthesis and must, therefore, acquire purines from the host milieu. Exploiting a mutant cell line (FBD5) of Leishmania donovani deficient in inosine and guanosine transport activity, the gene encoding this transporter (LdNT2) has been cloned by functional rescue of the mutant phenotype. LdNT2 encodes a polypeptide of 499 amino acids that shows substantial homology to other members of the equilibrative nucleoside transporter family. Molecular analysis revealed that LdNT2 is present as a single gene copy within the leishmanial genome and encodes a single transcript of 3 kilobase pairs. Transfection of FBD5 parasites with LdNT2 re-established their ability to take up inosine and guanosine with a concurrent restoration of sensitivity to the inosine analog formycin B. Kinetic analyses reveal that LdNT2 is highly specific for inosine (K(m) = 0.3 micrometer) and guanosine (K(m) = 1.7 micrometer) and does not recognize other naturally occurring nucleosides. Expression of LdNT2 cRNA in Xenopus oocytes significantly augmented their ability to take up inosine and guanosine, establishing that LdNT2 by itself suffices to mediate nucleoside transport. These results authenticate genetically and biochemically that LdNT2 is a novel nucleoside transporter with an unusual and strict specificity for inosine and guanosine.

Soret spectroscopic and molecular graphic analysis of human semi-beta-hemoglobin formation

The interaction of heme-free alpha (alpha(o)) and heme-containing beta (beta(h)) chains of human hemoglobin has been monitored in 0.1 M potassium phosphate buffer, pH 7 or 8, at 5 degrees C. Soret zero and first-derivative spectra were consistent with a uniform association reaction. Stopped-flow investigations demonstrated association rates on the order of 10(7) M(-1) s(-1). This was 100-fold more rapid than the reported rate of combination of alpha(h) and beta(h) proteins. This encounter-like rate of semi-beta-hemoglobin (alpha(o)beta(h)) formation was increased by raising the pH from 7 to 8. pH change is known to affect the spatial arrangement of AB-GH helical entities. Molecular graphic analysis of modeled alpha(o) protein superimposed over native alpha(h) protein revealed an apo Mb-like structure with well-defined AB-GH segments. Repositioning of these core helical segments, resulting in increased conformational freedom of the alpha1beta1 interface, was apparently responsible for the enhanced association properties of the alpha(o) protein.

Prospective evaluation of unexplained chronic liver transaminase abnormalities in asymptomatic and symptomatic patients

OBJECTIVES

It is currently recommend to perform a liver biopsy for patients with chronically elevated liver function tests (LFT) of unknown etiology (marker negative). The necessity and benefits of these recommendations are unknown. The aims of this study were to determine the prevalence of marker-negative LFT in patients referred for evaluation of chronically elevated LFT; to determine the prevalence of diseases that may be associated with marker-negative abnormal LFT; and to assess whether a liver biopsy alters the management of such patients.

METHODS

We conducted a prospective observational study of 1124 adults referred for evaluation of chronically elevated LFT. Patients who consented to a liver biopsy were eligible. Marker-negative abnormal LFT was defined as the absence of accepted serum markers for infectious, metabolic, autoimmune, or hereditary liver disease, the absence of a history of alcohol or hepatotoxic drug use, and the absence of signs of chronic liver disease.

RESULTS

Eighty-one of 1124 eligible patients were marker-negative. Liver biopsies in the 81 marker-negative patients revealed: normal histology (eight), steatosis (41), steatohepatitis (26), fibrosis (four), and cirrhosis (two). All 73 abnormal liver biopsies had some degree of steatosis. There were no significant associations between histological findings and the presence of obesity (p = 0.13), hyperlipidemia (p = 0.4), or diabetes (p = 0.9). There were no significant associations when classifying patients by gender or by symptoms.

CONCLUSION

In the setting of marker-negative elevated LFT, the most likely histological diagnosis is fatty metamorphosis of the liver with occasional associated fibrosis.

Cloning of Leishmania nucleoside transporter genes by rescue of a transport-deficient mutant

All parasitic protozoa studied to date are incapable of purine biosynthesis and must therefore salvage purine nucleobases or nucleosides from their hosts. This salvage process is initiated by purine transporters on the parasite cell surface. We have used a mutant line (TUBA5) of Leishmania donovani that is deficient in adenosine/pyrimidine nucleoside transport activity (LdNT1) to clone genes encoding these nucleoside transporters by functional rescue. Two such genes, LdNT1.1 and LdNT1.2, have been sequenced and shown to encode deduced polypeptides with significant sequence identity to the human facilitative nucleoside transporter hENT1. Hydrophobicity analysis of the LdNT1.1 and LdNT1.2 proteins predicted 11 transmembrane domains. Transfection of the adenosine/pyrimidine nucleoside transport-deficient TUBA5 parasites with vectors containing the LdNT1.1 and LdNT1.2 genes confers sensitivity to the cytotoxic adenosine analog tubercidin and concurrently restores the ability of this mutant line to take up [3H]adenosine and [3H]uridine. Moreover, expression of the LdNT1.2 ORF in Xenopus oocytes significantly increases their ability to take up [3H]adenosine, confirming that this single protein is sufficient to mediate nucleoside transport. These results establish genetically and biochemically that both LdNT1 genes encode functional adenosine/pyrimidine nucleoside transporters.

Analysis of the global architecture of hemoglobin A2 by heme binding studies and molecular modeling

The kinetics of CNProto- and CNDeutero-hemin binding to apohemoglobin A2 was investigated in a stopped-flow device in 0.05 M potassium phosphate buffer, pH 7, at 10 degrees C. The overall kinetic profile exhibited multiple phases: Phases I-IV corresponding with heme insertion (8.5-13 x 10(7) M(-1) s(-1)), local structural rearrangement (0.21-0.23 s(-1)), global alphadelta structural event (0.071-0.098 s(-1)), and formation of the Fe-His bond (0.009-0.012 s(-1)), respectively. Kinetic differences observed between apohemoglobin A2 and apohemoglobin A (previously studied) prompted an analysis of the structures of beta and delta chains through molecular modeling. This revealed a structural repositioning of the residues not only at, but also distant from the site of the amino acid substitutions, specifically those involved in the heme contact and subunit interface. A significant global change was observed in the structure of the exon-coded 3 region and provided additional evidence for the designation of this as the subunit assembly domain.

Fluorescence studies of human semi-beta-hemoglobin assembly

The intrinsic fluorescence properties of human alpha apohemoglobin at protein concentrations from 1 to 5 microM in 0.1 M potassium phosphate buffer, pH 7 or 8 at 5 degrees C were monitored in the absence and presence of a fixed concentration (5 microM) of a fluorescence quenching heme-containing native or Des (146-His, 145-Tyr) beta chain partner. These "reverse quenching" studies revealed that the emission intensity changes observed correlated well with protein concentration and theoretical extent of semi-beta-hemoglobin assembly. Furthermore, the relative quenching efficiencies were calculated to be 0.32, 0.25 and 0.61 for beta (pH 7), beta (pH 8) and Des beta (pH 7) chains, respectively. Thus, heme-mediated quenching was sensitive to the expected pH induced alpha apohemoglobin conformational change and to alteration in beta chain structure. Intramolecular changes induced by carboxylterminal modification (decreased "beta chain self-quenching") appeared to enhance the intermolecular rearrangements (increased "alpha chain partner quenching") seen upon subunit assembly.

Spectral demonstration of semihemoglobin formation during CN-hemin incorporation into human apohemoglobins

The incorporation of CN-hemin into three human adult apohemoglobin species (apohemoglobin, alpha-apohemoglobin, and apohemoglobin modified at its beta93 sulfhydryl with p-hydroxymercuribenzoate) has been monitored at micromolar concentrations in 0.05 M potassium phosphate buffer, pH 7.0, at 10 degrees C. In all cases, Soret spectral blue shifts accompanied CN-protohemoglobin but not CN-deuterohemoglobin formation. This finding in conjunction with isofocusing studies provided evidence of a CN-protosemi-alpha-hemoglobin intermediate, the formation of which appeared to be a direct consequence of CN-protohemin-alpha heme pocket interactions. The kinetics of full reconstitution of CN-protohemoglobin and CN-deuterohemoglobin revealed four distinct phases that apparently correlated with heme insertion (Phase I), local structural rearrangement (Phase II), global conformational response (Phase III), and irreversible histidine iron bond formation (Phase IV). These phases exhibited rates of 7.8-22 x 10(7) M(-1) s(-1), 0.19-0.23 s(-1), 0.085-0.12 s(-1), and 0.008-0.012 s(-1), respectively. Partial (50%) reconstitution with CN-protohemin, in contrast, revealed only three kinetic phases (with Phase III missing) of heme incorporation into native and p-hydroxymercuribenzoate-modified apohemoglobin. Furthermore, the absence of Phase III slowed the rate of proximal bond formation. These findings support the premise that irreversible assembly of CN-protosemi-alpha-hemoglobin is deterred by the presence of a heme-free beta partner, the consequence of which may be that intermolecular heme transfer is encouraged under conditions of heme deficiency in vivo.

Carboxyl-terminal modification influences subunit assembly of sickle hemoglobin beta chains

The subunit assembly properties of isolated beta and Des(His-146,Tyr-145) beta chains of sickle hemoglobin were investigated by isoelectric focusing over a protein concentration range from 500-125 microM in heme. Two components (presumably tetramer and monomer) and three components (designated tetramer, dimer and monomer) were visualized for beta s and Des(His-146,Tyr-145) beta s chains, respectively. Intensitometric quantitation of Des(His-146,Tyr-145) beta s chains demonstrated a similar distribution of all three structural components before and after the addition of their heteropartner alpha chains. This is in direct contrast to the reported preferential loss of Des(His-146,Tyr-145) beta A monomer species upon assembly and points to a major role of the beta 6 residue in the overall structural homeostasis of carboxylterminal modified human beta chains.

Use of serum bactericidal activity in assessing previous antibiotic therapy in acute lower respiratory tract infection in children

Bactericidal activity in sera of children with acute lower respiratory tract infection was assayed to determine its effect on the outcome of blood culture. Parental reporting of prior antibiotic therapy was also determined. 14.4% of samples without serum bactericidal activity yielded pathogens from blood culture, whereas only 2.4% of samples with serum bactericidal activity yielded pathogens. A statistically significant correlation was found between isolation of pathogens by blood culture and serum bactericidal activity. Parental reporting could not be relied upon as there was no positive correlation.

Genital standards for south Indian male newborns

One hundred and thirty-five male newborns in JIPMER hospital were studied. The penile length (stretched and unstretched), width as well as testicular length and breadth were measured. The influence of the gestational age and intrauterine growth on these measurements were studied. The mean stretched penile length for term babies was 3.57 cms (+/- 0.46), the unstretched length 3.26 cms (+/- 0.41), and the width was 1.04 cms (+/- 0.15). There was a linear increase in the above measurements with increasing gestational age. The right testicular length was 1.39 cms (+/- 0.28) and breadth was 0.98 cm (+/- 0.15) while the length and breadth for left testis were 1.32 cms (+/- 0.24) and 0.95 cm (+/- 0.14) respectively for term babies. The prepucial type was tubular in 103 (76.3%) babies and of ring type in 32 (23.7%). In 72 (53.3%) babies the prepuce could be retracted enough to visualise external urinary meatus.

Echographic-quantified severity of mitral anulus calcification: prognostic correlation to related hemodynamic, valvular, rhythm, and conduction abnormalities

Clinical and echocardiographic findings in 123 patients with mitral anulus calcification (MAC) were analyzed. In all patients M-mode echocardiography demonstrated a dense band of echoes posterior to the mitral valve, moving parallel and anterior to the left ventricular endocardium. Thirty-three per cent of patients were classified as having minimal to mild MAC (< 5 mm) and 67% had moderate to severe MAC (greater than or equal to 5 mm). There was a significant correlation between the degree of MAC to left atrial enlargement, congestive heart failure, aortic valve sclerosis, mitral regurgitation, atrial fibrillation, and AV-fascicular conduction defects. ECG evidence of conduction disturbances was significantly associated with MAC greater than or equal to t mm in width. The echocardiographic demonstration of MAC greater than or equal to 5 mm was significantly associated with the clinical implications known to occur with MAC; this echographic finding has important prognostic value in the evaluation of patients with mitral anulus calcification.

Alternating Wenckebach periods with acute myocardial infarction. Report of two cases

This report describes two patients with the spontaneous occurrence of alternating Wenckebach periods during the course of acute myocardial infarction. Both patients demonstrated alternating Wenckebach periods which terminated in a sequence of two blocked P waves. In one patient, His bundle electrocardiographic study documented the site of block to be proximal to the His bundle. Alternating Wenckebach periods with the block proximal to the His bundle may be compatible with a benign prognosis.

Lactic dehydrogenase isoenzyme determination in the diagnosis of acute myocardial infarction

Lactic dehydrogenase (LD) isoenzymes were determined by a rapid, simple technique and their utility in the diagnosis of acute myocardial infarction (AMI) was evaluated. LD isoenzymes were separated by ion-exchange column chromatography using DEAE-Sephadex. The cardiac fractions (LD-1 and LD-2) were measured separately on an Abbott ABA-100 analyzer and ratio of LD isoenzyme 1 to LD isoenzyme 2 (LD1:2) calculated. Daily serum samples were obtained from 100 patients selected only for a history of chest pain of abrupt onset. In 47 patients whose diagnosis was acute myocardial infarction (AMI), confirmed by typical clinical presentation and typical rise in cardiac-specific creatine kinase isoenzyme (MB(, peak LD1:2 ranged from 0.77 to 2.26. In 44 patients without AMI, peak LD1:2 ranged from 0.25 to 0.76. In two patients with electrocardiographic changes chest pain occurred two and five days previously; there was no rise in MB, but LD1:2 was elevated. Four patients with small AMI had no rise in LD1:2. Three more patients (one with active hemolysis) had false positive results. Thus, there was a sensitivity of 96% and a specificity of 97% when the cut-off point was LD1:2 = 0.76. LD1:2 is not quite as sensitive or specific as MD, but the ratio allows for the diagnosis of infarction in cases where MB has already returned to normal.