Overview of trials on artificial intelligence algorithms in breast cancer screening - A roadmap for international evaluation and implementation.

Accumulating evidence from retrospective studies demonstrate at least non-inferior performance when using AI algorithms with different strategies versus double-reading in mammography screening. In addition, AI algorithms for mammography screening can reduce work load by moving to single human reading. Prospective trials are essential to avoid unintended adverse consequences before incorporation of AI algorithms into UK's National Health Service (NHS) Breast Screening Programme (BSP). A stakeholders' meeting was organized in Newnham College, Cambridge, UK to undertake a review of the current evidence to enable consensus discussion on next steps required before implementation into a screening programme. It was concluded that a multicentre multivendor testing platform study with opt-out consent is preferred. AI thresholds from different vendors should be determined while maintaining non-inferior screening performance results, particularly ensuring recall rates are not increased. Automatic recall of cases using an agreed high sensitivity AI score versus automatic rule out with a low AI score set at a high sensitivity could be used. A human reader should still be involved in decision making with AI-only recalls requiring human arbitration. Standalone AI algorithms used without prompting maintain unbiased screening reading performance, but reading with prompts should be tested prospectively and ideally provided for arbitration.

Phagocytosis of Legionella pneumophila is mediated by human monocyte complement receptors.

We have examined receptors mediating phagocytosis of the intracellular bacterial pathogen, Legionella pneumophila. Three mAbs against the type 3 complement receptor (CR3), which recognizes C3bi, inhibit adherence of L. pneumophila to monocytes by 64 +/- 8% to 74 +/- 11%. An mAb against the type 1 complement receptor (CR1), which recognizes C3b, inhibits adherence by 68 +/- 1%. mAbs against other monocyte surface antigens do not significantly influence adherence. Monocytes plated on substrates of L. pneumophila membranes modulate their CR1 and CR3 receptors but not Fc receptors; such monocytes bind 70% fewer C3b-coated erythrocytes and 53% fewer C3bi-coated erythrocytes than control monocytes. Adherence of L. pneumophila to monocytes in nonimmune sera is dependent on heat-labile serum opsonins; adherence is markedly reduced in heat-inactivated serum (84% reduction) or buffer alone (97% reduction) compared with fresh serum. mAbs against CR1 and CR3 receptors also inhibit L. pneumophila intracellular multiplication and protect monocyte monolayers from destruction by this bacterium. This study demonstrates that human monocyte complement receptors, CR1 and CR3, mediate phagocytosis of L. pneumophila. These receptors may play a general role in mediating phagocytosis of intracellular pathogens.

Vitamin K deficiency in newborns: a case report in alpha-1-antitrypsin deficiency and a review of factors predisposing to hemorrhage.

A 4-week-old, breast-fed female infant appeared healthy until signs and symptoms of CNS deterioration suddenly occurred. At presentation the infant was found to have a left-sided parietal intracerebral hematoma, markedly prolonged prothrombin time, and partial thromboplastin time, normal platelet count, and jaundice with a total and direct serum bilirubin level of 5.4 mg/dL and 2.6 mg/dL, respectively. Vitamin K1 and fresh frozen plasma returned the prothrombin time and partial thromboplastin time to normal values within 18 hours, suggesting that the infant had severe vitamin K deficiency complicated by intracerebral hemorrhage. Evaluation of the infant's direct hyperbilirubinemia led to the diagnosis of homozygous (pi-type ZZ [PiZZ] ) alpha-1-antitrypsin deficiency. The clinical circumstances predisposing to vitamin K deficiency in newborns and infants are discussed. Based on our observations in this case, we suggest that cholestatic liver disease should be suspected when unexplained vitamin K deficiency occurs in early infancy. The role of vitamin K in hemostasis and the laboratory diagnosis of vitamin K deficiency are discussed as they apply to the evaluation of hemorrhage in newborns and infants.

Correlation of clinical and pathologic findings in early onset neonatal group B streptococcal infection with disease severity and prediction of outcome.

This study analyzed the clinical characteristics of 69 neonates who were admitted to the University of Minnesota Hospital between January, 1972, and June, 1984, with early onset Group B streptococcal infection (EOGBS) and determined those features associated with fatal infection. The incidence of EOGBS was 1.6 cases/1000 live births among 7960 inborn infants; the mortality rate for inborn and outborn infants was 28%. Multivariate analysis identified five features adequately predicting fatal outcome: birth weight less than 2500 g, absolute neutrophil count less than 1500 cells/mm3, hypotension, apnea and a pleural effusion on the initial chest radiographs. With these five variables and an initial blood pH less than 7.25, a clinical score was constructed that correctly predicted outcome in 93% of patients in this study (87% sensitivity, 95% specificity). Autopsy findings in 16 of 19 infants with fatal EOGBS suggested that surfactant deficiency respiratory distress syndrome was common in preterm infants with EOGBS and contributed to their higher mortality compared with term infants.

Rapid identification of respiratory syncytial virus infections by direct fluorescent antibody testing: reliability as a guide to patient cohorting.

This study compared the results of a commercially available, direct fluorescent antibody (DFA) test with viral culture in 880 specimens obtained from 690 patients by means of nasopharyngeal swabs. The two tests were congruent in 92.5% (814) of the specimens. The sensitivity of the DFA was 0.95, the specificity was 0.91, the positive predictive value was 0.82, and the negative predictive value was 0.98. Among 548 inpatients, there were 3 mixed infections (RSV and another virus), 8 RSV infections not identified by the DFA, and 35 positive DFA results not confirmed by cell culture. Use of the DFA test alone would have resulted in 502 (92%) correct patient-placement decisions. We conclude that the DFA test provides reliable evidence on which to base patient-placement decisions but that the error rate is too high to permit safe cohorting of high-risk patients, such as those with bronchopulmonary dysplasia.

Congenital diaphragmatic hernia in Minnesota. Impact of antenatal diagnosis on survival.

OBJECTIVE: We characterized the natural history and true mortality of congenital diaphragmatic hernia (CDH) in newborn patients by identifying all infants born with this condition in a fixed geographic region over a 2-year period. We examined this population to determine the frequency of intrauterine diagnosis, the outcome of prenatally diagnosed infants, and the impact of deaths in infants with an unsuspected diagnosis (the "hidden mortality") on the overall outcome of this condition. DESIGN: This was a retrospective population survey of all infants born with CDH in Minnesota between June 1988 and June 1990. SETTING: All Minnesota birth and death records were reviewed to identify patients with the diagnosis of CDH. A separate survey of all level 3 intensive care nurseries was conducted and the record of each identified patient was reviewed. Extracorporeal membrane oxygenation was available throughout the study period. MAIN OUTCOME MEASURE: Survival to hospital discharge and short-term morbidity were examined for each patient. RESULTS: Survival was 60% (29/48). Eleven of 19 deaths occurred in patients born prematurely and/or with coexisting major anomalies. Eight percent (4/48) of patients died within the first hour of life prior to diagnosis (hidden mortality). Intrauterine diagnosis of CDH was made in 15 patients. Survival was 60% (9/15) in infants whose conditions were diagnosed in utero, a rate identical to that for infants whose conditions were diagnosed in the postnatal period (61% [20/33]). There was no relationship between age at fetal diagnosis and mortality. CONCLUSIONS: The hidden mortality of CDH was low. Almost half of the total mortality for CDH was associated with coexisting, additional anomalies. Patients who were not offered extracorporeal membrane oxygenation owing to prematurity, other major anomalies, or birth at a center that did not offer extracorporeal membrane oxygenation accounted for 84% (16/19) of deaths. These data will be useful for determining the impact of new therapeutic strategies on the mortality of CDH.

Comparison of six ECMO selection criteria and analysis of factors influencing their accuracy.

This study compared six extracorporeal membrane oxygenation (ECMO) selection criteria in 42 neonates and analyzed factors influencing the accuracy of outcome predictions. The sensitivity of the criteria in identifying fatal cases varied from 0.44 to 0.94 and the specificity of predictions of survival ranged from 0.42 to 0.69. The criterion having the highest sensitivity had the lowest specificity and conversely the criterion with the lowest sensitivity had the highest specificity. Overall accuracy of the criteria, as measured by the total number of correct outcome predictions, differed little among the criteria (23/42 to 27/42 correct predictions). Three factors influenced predictive accuracy: 1) a primary diagnosis of congenital diaphragmatic hernia (CDH) was associated with a greater mortality (P less than 0.001) and a significantly higher positive predictive value (PPV) for all criteria (P = 0.0009-0.012) than that seen in patients with other primary diagnoses; 2) calculating the alveolar-arterial oxygen gradient using an assumed, rather than measured barometric pressure, or estimating oxygenation index using a calculated, rather than a measured, mean airway pressure, increased false positive mortality predictions in non-CDH patients; and 3) requiring a peak inspiratory pressure (PIP) of at least 50 cm H2O in the definition of maximal medical management, rather than a PIP of 20-49 cm H2O, significantly increased the PPV for three of four criteria examined (P = 0.02-0.04). Awareness of these factors may facilitate the identification of neonates who need ECMO to survive.

Spontaneous, isolated intestinal perforations in neonates with birth weight less than 1,000 g not associated with necrotizing enterocolitis.

From January 1986 through December 1988, we have seen 7 cases of isolated intestinal perforation in 250 infants with birth weights less than 1,000 g (3% incidence) without histological or clinical evidence of necrotizing enterocolitis (NEC). Patients had a mean birth weight of 670 g, gestational age of 25.1 weeks, and sustained a perforation at a chronological age of 10.4 days. No infants had been fed. A definite, blue-discolored abdomen was the only consistent clinical sign (n = 7). Free intraperitoneal air on radiograms was rarely observed (n = 1). Abdominal ultrasounds (n = 3) and metrizamide contrast studies (n = 3) were not diagnostic. The presence of an umbilical artery catheter (7/7), falling hematocrit (6/7), thrombocytopenia (5/7), and a positive diagnostic paracentesis were most commonly found. In 6 of 7 patients, this perforation was associated with coagulase-negative staphylococcal sepsis. Surgical or histological diagnosis showed focal perforation in either the terminal ileum (n = 4) or the transverse and descending colon (n = 3). Survival was 3 of 7; 2 patients died of intracranial hemorrhage and 2 died of Candida sepsis. We conclude that (1) intestinal perforation can occur in the absence of NEC; (2) bluish discoloration of the abdomen is the most reliable clinical finding; and (3) perforation may be associated with coagulase-negative staphylococcal infection.

Activated clotting time tests with heparinase in the management of pediatric patients on cardiopulmonary bypass.

Routine ACT tests cannot distinguish between prolonged blood clotting due to heparin effect or acquired abnormalities of the coagulation system after a loading dose of heparin. The purpose of this study was to examine an ACT test that inactivates heparin with Heparinase allowing for ACT assessment with and without heparin effect (HR-ACT with/without Heparinase, HemoTec, Inc.). The HR-ACT values were compared with the standard OR procedure that employed the Hemochron ACT. Twenty pediatric patients undergoing cardiopulmonary bypass for repair of cardiac defects were examined. All comparative ACT values were obtained from the same blood sample. Five sampling times were examined: 1) A baseline ACT was obtained before heparin had been administered; 2) A pre bypass ACT after a single heparin dose; 3) On bypass; 4) A post protamine ACT at the conclusion of surgery; and 5) In the Intensive Care Unit (PICU), 1 hour post protamine. The HemoTec HR-ACT with Heparinase and HR-ACT tests differentiated clotting time results that reflected coagulation status without the heparin effect. It identified those patients on bypass who were less than 5 kg, with prolonged ACTs that were due in part to hemodilution despite efforts at hemoconcentration.

Predictive performance of three methods of activated clotting time measurement in neonatal ECMO patients.

Previously reported activated clotting time (ACT) data in adults demonstrated higher values with the HemoTec LRACT (HT) and TriMed ACTivator (TM) techniques than with the Hemochron System P214/215 (HC) technique throughout a range of heparin concentrations. This study sought to determine if a difference exists in ACT values of neonatal patients receiving ECMO. ACTs were performed in nine neonatal ECMO patients using the HC, HT, and TM techniques. Techniques were compared for positive or negative direction of any prediction difference (bias), and the typical value of a difference (precision). Simultaneous, duplicate, morning, and afternoon ACT comparisons were obtained using all three techniques. Forty-six comparisons of HC values in the 180-240 sec range were analyzed. All techniques produced results different from the same sample. The HT and TM techniques were upwardly biased by 51 and 148 sec, respectively, when evaluated against HC. HT was negatively biased by 123 sec when evaluated against TM. Because ACT values vary among techniques, ACT target ranges should be technique specific. Future references to ACT data should identify the equipment and procedures employed.

The relation of the Ibc protein antigen to the opsonization differences between strains of type II group B streptococci.

Thirty-one type II and eight nontypable group B streptococcal isolates were categorized by the presence of the trypsin-resistant and trypsin-sensitive components of the Ibc protein antigen and studied for opsonization differences by using polymorphonuclear leukocyte chemiluminescence (CL). Type II strains varied in their ease of opsonization: strains possessing both components of the Ibc protein elicited a significantly lower mean CL peak (P less than or equal to .05) and a smaller CL integral (P less than or equal to .01) than did type II strains lacking both components or strains lacking type polysaccharide antigen but possessing the Ibc protein antigen. These strain differences were seen consistently with different sera and were also observed in an opsonophagocytic killing assay. Differences in opsonizing ability and bacterial killing were found for three standard test sera but could not be related to the concentration of type-specific antibody to capsular polysaccharide antigen. Our studies suggested that the Ibc protein antigen was one factor that contributed to the resistance to opsonization of strains of type II group B streptococci.

Extremely low birth weight infants have lower Fc gamma RIII (CD 16) plasma levels and their PMN produce less Fc gamma RIII compared to adults.

The purpose of this study was to determine whether decreased Fc gamma RIII expression on the PMN of extremely low birth weight infants (ELBW) is due to decreased receptor synthesis or increased receptor shedding from the PMN surface. 42 ELBW, 12 larger infants and 14 adults were enrolled. Plasma and total cellular Fc gamma RIII were measured by ELISA, and PMN Fc gamma RIII expression was measured by flow cytometry. ELBW PMN plasma membrane expression of Fc gamma RIII as measured by log mean channel fluorescence (5.00 +/- 1.98 vs. 10.68 +/- 1.61, p < 0.050) and plasma Fc gamma RIII levels were both lower (7.5 +/- 6.1 vs. 82.4 +/- 64.8 nM, p < 0.05) than in adult controls. In follow-up studies, 14 ELBW (age = 29 +/- 14 days, range = 14-56 days) increased PMN expression of Fc gamma RIII (p < 0.001) but not plasma Fc gamma RIII. ELBW had lower total PMN-associated Fc gamma RIII than adults (2.3 +/- 0.9 vs. 6.8 +/- 2.2 ng/10(6) PMN, p = 0.006). ELBW's PMN produce less Fc gamma RIII than adults' PMN, and expression of this receptor is developmentally regulated.

Opsonic effect of jacalin and human immunoglobulin A on type II group B streptococci.

This study examined the effect of immunoglobulin A (IgA) and the IgA-binding lectin jacalin on the phagocytosis of type II group B streptococci (GBS). Strains possessing the trypsin-sensitive and trypsin-resistant components of the c protein (II/c) and type II GBS lacking the c protein (II) were examined by radiolabeled bacterial uptake, bactericidal assays, and electron microscopy. Type II/c GBS resisted phagocytosis by monocytes (4.9% +/- 0.8% uptake, mean +/- SE, n = 25) compared with type II GBS (8.5% +/- 1.4% uptake, n = 14, P = 0.03). Phagocytic killing by polymorphonuclear leukocytes was also less for the type II/c strain 78-471 than for the type II strain 79-176 (68% +/- 5% versus 86% +/- 4% reduction in CFU at 45 min, P = 0.03). IgA binding did not explain the resistance of type II/c GBS to phagocytosis. The uptake of type II/c GBS was not significantly different after opsonization in cord sera lacking endogenous IgA (5.93% +/- 1.4%) than in the same cord sera after addition of exogenous IgA (5.48% +/- 1.4%, P = 0.69, n = 9). Attempts to remove serum IgA with the IgA-binding lectin jacalin resulted in the binding of IgA-jacalin complexes to II/c GBS. This combination of nonspecific IgA and jacalin increased uptake of II/c GBS from 4.9% +/- 0.8% to 11.8% +/- 1.9% (P = 0.002). Jacalin also combined with specific, immune, monoclonal IgA bound to the surface of Haemophilus influenzae and promoted the uptake of these bacteria. Jacalin and IgA mediated phagocytosis of II/c GBS via receptors that were not dependent on divalent cations and that were not modulated by plating monocytes on antigen-antibody complexes.

Cell-surface expression of immunoglobulin G receptors on the polymorphonuclear leukocytes and monocytes of extremely premature infants.

This study measured Fc gamma receptor (FcR) expression on polymorphonuclear leukocytes (PMN) and monocytes from extremely premature infants. Flow cytometry was used to quantitate FcRIII [cluster of differention (CD) 16], FcRII (CD32), FcRI (CD64), CD14, and CD67 proteins on the PMN surface. Sixty-four premature infants with a mean gestational age +/- SD of 26 +/- 2 wk (birth weight = 847 +/- 217 g), 12 infants born at term (gestational age = 38 +/- 1 wk), and 37 adults were studied. Premature infants' PMN expressed less FcRIII, measured as mean log channel fluorescence (MCF), than did term infants or adults (MCF = 4.7 +/- 1.4, 6.1 +/- 1.0, and 8.8 +/- 1.8, respectively, p < 0.050). Premature infants also had a lower proportion of FcRIII-positive PMN than term infants or adults (mean +/- SEM = 0.83 +/- 0.02 versus 0.92 +/- 0.04 and 0.96 +/- 0.01, respectively, p < 0.050). FcRIII expression on PMN was positively associated with cell isolation procedures (p = 0.004), birth weight (p = 0.004), and postnatal age (p = 0.032). Premature infants also had lower PMN expression of FcRII when compared with adults and term infants (MCF = 2.4 +/- 0.6 versus 3.0 +/- 0.7 and 3.1 +/- 0.3, p < 0.050). Both premature and term infants had fewer FcRII positive PMN than did adults (mean +/- SEM = 0.90 +/- 0.09 and 0.89 +/- 0.07 versus 0.99 +/- 0.00, p < 0.050). Premature infants' monocytes also expressed significantly less FcRIII (MCF = 2.4 +/- 0.6 versus 3.4 +/- 0.9, p = 0.047) and FcRII (2.1 +/- 0.5 versus 2.9 +/- 0.6, p = 0.01) compared with adults. We conclude that extremely premature infants have decreased expression of FcRIII and FcRII on both their PMN and monocytes when compared with adults. The decrease in PMN FcRIII expression appears related to birth weight and chronologic age.

Effects of surfactant therapy on outcome of extremely premature infants.

Limits of viability of extremely premature infants have recently been addressed both in Europe and the United States. These reports, which demonstrate frequent adverse outcome of infants born before 26 weeks of gestation, have not considered the impact of surfactant therapy. We reviewed records of 445 infants born between 23 and 36 weeks gestation who were admitted to our nursery following the availability of surfactant treatment in 1986 through 1992. Two hundred and eighty-five infants were treated with surfactant (Survanta, Ross Laboratories) as part of controlled, prospective trials or as routine treatment under Food and Drug Administration approval. One hundred and fifty-six infants were unable to be treated with surfactant, as either they received placebo therapy during prospective trials or were born prior to approval of routine surfactant use in the United States. Four additional infants born following the commercial availability of surfactant did not receive surfactant therapy. Survival of untreated infants was 56% compared to 75% in treated infants (P < 0.001). Infants born at all gestational ages between 23 and 26 weeks had an increased likelihood of survival as a result of surfactant treatment. No differences in neurologic outcome between surfactant treated and non-treated infants were demonstrated at subsequent follow-up. We conclude that survival of extremely premature infants is improved following surfactant therapy and that subsequent neurologic outcome is not compromised as a result of this therapy.

Effect of differences in antibody and complement requirements on phagocytic uptake and intracellular killing of "c" protein-positive and -negative strains of type II group B streptococci.

The influence of antibody and complement on the polymorphonuclear leukocytic uptake and killing of type II group B streptococci (GBS) was examined with 11 adult sera and three type II strains possessing the trypsin-resistant and trypsin-sensitive components (II/TR+TS) of the "c" (formerly Ibc) protein or two type II strains lacking both components (II/no c) of the c protein. All tested sera mediated a greater than 1 log10 reduction in colony-forming units (CFUR) of a type II/no c strain, even in the absence of measurable type-specific antibody (less than 1.08 micrograms/ml), but only 5 of 11 mediated a greater than 1 log10 CFUR of any type II/TR/TS strain, even in the presence of moderate levels of type-specific antibody. The classical pathway of complement activation appeared to be more important than the alternative pathway, and even absorbed or immunoglobulin G (IgG)-depleted serum (IgG, 10 mg/dl) mediated a greater than 1 log10 CFUR without magnesium ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (magnesium EGTA) chelation. Chelation with magnesium EGTA reduced the CFUR in 4 of 11 test sera and greatly reduced the CFUR in absorbed or IgG-depleted sera for type II/no c strains. Despite variation in the phagocytic killing of two representative strains of type II GBS, both strains were well phagocytized, as measured by radiolabeled bacterial uptake or electron microscopy. This study suggested that poorly killed type II/TR+TS GBS were easily phagocytized but apparently resisted intracellular killing.

Selecting antibiotics for nosocomial bacterial infections in patients requiring neonatal intensive care.

Nosocomial infections increase neonates' morbidity, hospital costs, and mortality. These infections occur most commonly in very low birth weight infants, who frequently required plastic intravascular catheters and parenteral nutrition. Diagnosis often relies on a combination of laboratory tests and nonspecific clinical signs. Criteria for diagnosing nosocomial infections have been published by the Centers for Disease Control (CDC) and should be used to standardize the identification of cases. Initial antibiotic therapy depends on (1) the bacterial species most likely to cause infection, (2) antibiotic resistance patterns in one's own hospital, (3) the patient's clinical condition, and (4) previous antibiotic therapy. Antibiotic coverage of both gram-positive and gram-negative bacteria is necessary. Following laboratory identification of the infecting organism and the antibiotic susceptibility results, the patient should be reevaluated and definitive therapy prescribed. Multiple antibiotics may be needed as definitive therapy if (1) the infecting organism is likely to develop resistant mutants during therapy (e.g., Pseudomonas species), (2) higher bactericidal serum activity is required than can usually be achieved with a single agent (e.g., enterococci, Listeria), (3) the patient is neutropenic or otherwise severely immunocompromised, or (4) blood cultures are persistently positive for bacteria despite appropriate therapy with a single agent. Attempts to prevent nosocomial bacteremias by routinely administering prophylactic vancomycin may hasten the development of vancomycin-resistant, coagulase-negative staphylococci or enterococci and should be avoided.

Nonimmune binding of human immunoglobulin A to type II group B streptococci.

The binding of 125I-labeled human myeloma immunoglobulin A (IgA) to four type II strains and one nontypable strain of group B streptococci was measured after streptococcal chains were broken by brief sonication. Some IgA binding was observed with all strains, but specific binding (binding that was inhibited by excess unlabeled IgA, was dose dependent, and was saturable) occurred only with those strains possessing the trypsin-sensitive beta component of the c protein. Similar amounts of binding were observed with myeloma IgA and IgA1 purified from normal serum. Specific binding was more rapid at 25 degrees C than at 0 or 37 degrees C and reached a plateau in 6 to 8 h. Binding was drastically reduced (85 to 90%) when streptococci had been heated (90 degrees C for 1 h). Most radioactivity bound to group B streptococci could be displaced (greater than 60% in 3 days) by the addition of excess unlabeled IgA. The binding capacity of one strain (10(8) streptococci in 1 ml of buffer) was saturated by approximately 24 micrograms of IgA. When transformed for Scatchard analysis, these data indicated that there was a specific binding capacity of 16,000 molecules of monomeric serum IgA per single streptococcal cell. The dissociation constant for IgA binding was 19.3 nM. Since enzyme-linked immunosorbent assay studies showed that the myeloma IgA used for the studies described above was IgA1, our quantitative data apply only to the binding of this subclass to group B streptococci. However, an enzyme-linked immunosorbent-filtration assay showed that both IgA1 and IgA2 bound to a type II group B streptococcus bearing the c protein.

Phagocytosis of Mycobacterium tuberculosis is mediated by human monocyte complement receptors and complement component C3.

We have examined the receptor-ligand interactions and the method of phagocytosis of virulent Mycobacterium tuberculosis by human monocytes. mAb against complement receptors (CR) inhibit adherence and phagocytosis of M. tuberculosis in fresh nonimmune serum. A mAb against the type 1 CR (CR1) inhibits adherence of M. tuberculosis by 40 +/- 5%, and three different mAb against the type 3 CR (CR3) each inhibit adherence by 39 +/- 5% to 47 +/- 4%. A mAb against CR1 used in combination with one of the three mAb against CR3 inhibits adherence by up to 64 +/- 7%. Most strikingly, two mAb used in combination against CR3 inhibit adherence by up to 81 +/- 2%. mAb against other monocyte surface Ag do not significantly influence adherence. In like fashion, mAb against CR but not other monocyte surface Ag inhibit adherence of preopsonized M. tuberculosis in the presence of heat-inactivated serum. By electron microscopy, monocytes ingest all M. tuberculosis that adhere in the presence of nonimmune serum; mAb against CR3 markedly inhibit ingestion. In contrast to CR, the FcR and the beta-glucan-inhibitable receptor for zymosan play little or no role in mediating M. tuberculosis adherence or ingestion. Adherence of M. tuberculosis is serum-dependent, requiring greater than or equal to 2.5% serum for optimal adherence. Heat inactivation of serum markedly reduces adherence of M. tuberculosis (75.5 +/- 7%) and preopsonization of bacteria enhances adherence by 2.9 +/- 0.4-fold. Adherence is also markedly reduced in C3- or factor B-depleted serum; repletion with C3 or factor B increases adherence by 2.1 +/- 0.4-fold and 1.86 +/- 0.05-fold, respectively. Fab anti-C3 IgG markedly inhibits monocyte adherence of preopsonized M. tuberculosis (71 +/- 1%). C component C3 is fixed to M. tuberculosis by the alternative C pathway as determined by a whole bacterial cell ELISA. Human monocytes ingest M. tuberculosis by conventional phagocytosis as viewed by electron microscopy. This study demonstrates that human monocyte CR1 and CR3 mediate phagocytosis of M. tuberculosis and C component C3 in serum is acting as the major bacterium-bound ligand.