William P. Reed

Host Defenses and Immunologic Alterations Associated with Chronic Hemodialysis

Many of the complications experienced by patients undergoing hemodialysis can be attributed to their altered host defenses. Increased cutaneous staphylococcal carriage along with repeated intravascular cannulation and defective mucocutaneous barriers lead to frequent invasion by infectious agents. Pathogens encounter granulocytes with subnormal locomotion, phagocytosis, and intracellular killing. Depressed cell-mediated immunity may be explained by shortened lymphocyte survival, lymphopenia, inhibition of lymphocyte transformation, and suppressor T-cell activity. This is manifested by cutaneous anergy, prolonged graft survival, altered tumor surveillance, and abnormal responses to hepatitis B and tuberculosis. Host interaction with the hemodialysis membrane leads to cellular disruption, which may induce autoantibodies. Activation of the alternate complement pathway during hemodialysis leads to granulocyte sequestration in small vessels, specifically within the lungs. These hemodialysis-induced alterations along with the manifestations of underlying chronic renal insufficiency may obscure clinical evaluation of these patients.

Resistance to infection of the external eye: The role of tears

The external eye is continuously exposed to an environment containing potentially pathogenic microorganisms. One of the mechanisms which protects the eye from infection is the tear layer. We review the current knowledge of those antimicrobial substances known to be present in tears and the role they might play in preventing infection. These substances include lysozyme, lactoferrin, beta-lysin, and the antibody-complement system of proteins.

Serum inhibitor of C5 fragment-mediated polymorphonuclear leukocyte chemotaxis associated with chronic hemodialysis.

Abnormal granulocyte chemotaxis has been described in chronic hemodialysis patients. In this study, sera from 53 hemodialysis patients were tested for chemotactic inhibitory activity by a modified Boyden technique. Chemotactic inhibitory activity, defined as >20% inhibition of normal granulocyte chemotaxis, was found in 45% of patients. Only sera from patients having undergone >3 mo hemodialysis displayed chemotactic inhibitory activity and retained this inhibitory activity when retested 9 mo later. Four of five patients who had initially undergone <3 mo hemodialysis and lacked serum chemotactic inhibitory activity developed inhibitory activity when tested 9 mo later. Clinical evaluation of patients with serum chemotactic inhibitory activity showed that these patients did not have a significantly increased incidence of infection, although a trend toward decreased mortality during the time of study was observed (P = 0.0721). Serum chemotactic inhibitory activity was heat stable at 56 degrees C for 30 min and concentration dependent. The major inhibitory component was found to have a sedimentation coefficient of 4S by sucrose density gradient centrifugation. The chemotactic inhibitory activity was not precipitated by 30% ammonium sulfate, but was partially precipitated by 50% ammonium sulfate. Inhibitory sera effectively suppressed neutrophil migration in response to chemotactic C5 fragment and Escherichia coli derived chemotactic factor but was least effective in a system mediated by casein. Furthermore, normal neutrophils preincubated in hemodialysis patient sera displayed normal chemotactic responsiveness indicating a lack of cell-directed inhibition. Serum fractions that contained the inhibitor were found to directly act on the chemotactic C5 fragment, reducing its chemotactic activity. This study indicates that a circulating 4S, heat-stable, factor-directed inhibitor of granulocyte chemotaxis is present in the sera of many hemodialysis patients and probably results from the hemodialysis procedure.

Pentoxifylline Relaxes Isolated Pulmonary Arteries after Preconstriction with Norepinephrine

Pentoxifylline (PTX) is a methylxanthine derivative which improves systemic microvascular flow and tissue oxygen delivery, presumably through actions on platelet aggregation and erythrocyte deformability. Although PTX also improves pulmonary vascular flow, recent evidence suggests that part of this improvement may be due to pulmonary vasodilation. To evaluate these effects we studied isolated rabbit lobar pulmonary artery (PA) ring segments to determine if PTX had direct effects on PA tissues and whether these effects could be modulated pharmacologically or by endothelial disruption. PTX had no effect on PA at resting tension. However, if the PA tension was actively increased by norepinephrine (5 microM), subsequent PTX application caused concentration-dependent PA relaxation. Relaxation occurred promptly and was maximal within 45-60 s. The threshold PTX concentration necessary for relaxation was 1 microM. PTX-induced relaxation was not affected by pretreatment with the cyclo-oxygenase inhibitor indomethacin (1 microM). Endothelial disruption by gentle rubbing of the intimal PA surface abolished relaxation of preconstricted PA by acetylcholine, but had no effect on relaxation by PTX. Although PA at resting tension displayed no response to PTX, PA constriction by norepinephrine in the presence of PTX concentrations greater than 10 microM was significantly decreased. These data indicate that PTX has direct actions on isolated rabbit PA which are not blocked by indomethacin nor require the presence of intact endothelium. Furthermore, PTX can suppress norepinephrine-induced constriction of isolated PA.

Differences in blood group B-specific mucinase activity between virulent and avirulent Shigella flexneri 2a strains

Based on our previous findings we postulate that the production of blood group B-degrading mucinase by Shigella flexneri 2a is related to virulence. The virulent S. flexneri 2a strain M4243 produced a blood group B mucinase which decreased the blood group B reactivity of germ-free mouse mucins by a factor of 16 and the B reactivity of human saliva by a factor of 32. Avirulent S. flexneri 2a B-1, serologically similar, but not genetically identical to the M4243 strain, failed to degrade the blood group reactivity. The mucin-degrading ability of S. flexneri 2a M4243 harboring a large virulence-conferring 140 MDa plasmid was then compared with a genetically similar large plasmid-free avirulent S. flexneri 2a M4243A1. Virulent S. flexneri M4243 grew in human salivary mucins while the genetically identical avirulent M4243A1 did not. Supernatant of virulent M4243 culture decreased the blood B reactivity of salivary mucins by a factor of 32 while the avirulent M4243a1 had no effect. Eleven of 12 colonies of the transconjugant hybrid Escherichia coli K12 (7300-1-5) containing the shigella PWR 110 plasmid and chromosomal markers decreased the blood group B reactivity by a factor of 4-32, and two of four colonies of the E. coli strain 7262 containing only the plasmid reduced the B reactivity by a factor of 4-16. These findings suggest that blood group B-specific mucinase production may be related to S. flexneri virulence.

Secretory IgA and Direct Killing of Shigella by Serum Components

Shigellosis is an enteric infection in which bacteria are restricted to the intestinal lumen and mucosa, and deeper systemic invasion is rare, even in nonimmune individuals. Spontaneous recovery is common, and subsequent resistance to reinfection may occur, but field trials with parenteral vaccines have shown systemic antibodies to be nonprotective. However, the effectiveness of oral vaccines suggests that local or intestinal immunity may exist. Since previous studies have shown large quantities of secretory IgA to be present in Shigella diarrhea stools (1), it seems possible that local immunity may be mediated by this immunoglobulin. The following studies investigate direct serum killing as one possible mechanism through which secretory IgA could exert an anti-Shigella effect.

Neutrophil responses to intravascular pneumococcal sonicate.

Leukopenia and pulmonary leukostasis are prominent features in patients succumbing to pneumococcal (PNC) infections. We examined mechanisms involved in recruitment of polymorphonuclear neutrophils (PMNs) into pulmonary capillaries and alveolae after PNC sonicate injection. We showed that by 15 min postinjection, PMN chemotactic activity was found in bronchoalveolar lavage (BAL) fluids and increased with time until the end point of the study at 90 min. Accompanying the increased chemotactic activity in BAL fluids was a decrease in circulating PMNs more pronounced in the femoral artery (FA) then the pulmonary artery (PA). Super-oxide anion (O2−) production by peripheral PMNs was depressed following PNC sonicate injection, and comparison of FA and PA showed that FA PMNs produced less O2− than PA PMNs. PA PMNs also showed enhanced random migration when compared to the depressed random migration of FA PMNs. This study demonstrated that an intravascular challenge of PNC sonicate was associated with increased chemotactic activity for PMNs in BAL fluid. Fewer PMNs and altered PMN function resulted from passage through the pulmonary microvasculature after PNC sonicate injection.

Depression of papillary muscle contractility by plasma incubated with pneumococci.

Mechanisms of death in pneumococcal disease are poorly understood. We have previously shown that intravenous pneumococcal products in dogs caused a mean decrease in cardiac output of 58%. The present study used measurements of the force and rate of contraction of isolated rabbit papillary muscle to determine whether pneumococci (PNC) altered myocardial contractility. Nine papillary muscles were superfused with various solutions including Tyrodes, Tyrodes incubated with sonicated type 1 PNC, normal rabbit plasma, and rabbit plasma incubated with PNC. Compared to untreated Tyrodes solution, PNC-treated Tyrodes solution did not alter papillary muscle contractility. However, compared to untreated rabbit plasma, plasma incubated with PNC caused a mean decrease of 18% in the force of contraction and 16.7% in the maximum rate of force development in nine studies. We conclude that PNC do not directly affect papillary muscle contractility. However, the interaction of PNC and plasma does cause a decrease in rabbit papillary muscle contractility.