THE PASSAGE OF RABBIT VIRULENT TYPE III PNEUMOCOCCI FROM THE RESPIRATORY TRACT OF RABBITS INTO THE LYMPHATICS AND BLOOD

Bacterial Lymphatic Metastasis in Infection and Immunity

Lymphatic vessels permeate tissues around the body, returning fluid from interstitial spaces back to the blood after passage through the lymph nodes, which are important sites for adaptive responses to all types of pathogens. Involvement of the lymphatics in the pathogenesis of bacterial infections is not well studied. Despite offering an obvious conduit for pathogen spread, the lymphatic system has long been regarded to bar the onward progression of most bacteria. There is little direct data on live virulent bacteria, instead understanding is largely inferred from studies investigating immune responses to viruses or antigens in lymph nodes. Recently, we have demonstrated that extracellular bacterial lymphatic metastasis of virulent strains of Streptococcus pyogenes drives systemic infection. Accordingly, it is timely to reconsider the role of lymph nodes as absolute barriers to bacterial dissemination in the lymphatics. Here, we summarise the routes and mechanisms by which an increasing variety of bacteria are acknowledged to transit through the lymphatic system, including those that do not necessarily require internalisation by host cells. We discuss the anatomy of the lymphatics and other factors that influence bacterial dissemination, as well as the consequences of underappreciated bacterial lymphatic metastasis on disease and immunity.

THE LYMPHATIC PATHWAY FROM THE NOSE AND PHARYNX : THE ABSORPTION OF DYES

1. In the monkey, dog, cat, and rabbit the cervical lymph duct was cannulated, and then a solution of T-1824, or trypan blue, or a fine graphite suspension, all in physiological saline, was dropped into the nose. T-1824 was used in all four animals, trypan blue in the cat and dog, the graphite suspension (Hydrokollag) in the cat alone. 2. No Hydrokollag was ever found in the cervical lymph. 3. Trypan blue and T-1824 appear in the cervical lymph 15 to 30 minutes after being placed in the nose of the cat and monkey, 51 to 53 minutes in the dog, and 14 minutes in the rabbit. 4. T-1824 and trypan blue were also absorbed from the nose directly into the blood. 5. Neither the dyes nor the Hydrokollag, though left in the nose for as long as 6 hours, were found to pass through the cribriform plate and reach the interior of the cranium. 6. In the monkey cervical lymph passes through a chain of five or more lymph nodes, in the rabbit frequently through two nodes, in the cat through one node except in rare instances, and in the dog through one node.

Effect of mechanical ventilation strategy on dissemination of intratracheally instilled Escherichia coli in dogs

OBJECTIVE

To test the effect of different mechanical ventilation strategies on dissemination of intratracheally instilled Escherichia coli in dogs and to determine the extent and distribution of lung damage.

DESIGN

Prospective, randomized study.

SETTING

Experimental animal laboratory.

SUBJECTS

Eighteen anesthetized and paralyzed dogs.

INTERVENTIONS

We studied the effect of three ventilatory strategies based on two variables: transpulmonary pressure and positive end-expiratory pressure (PEEP). Group 1 animals (n = 6) were ventilated with a PEEP of 3 cm H2O and a tidal volume of 15 mL/kg, which generated an end-inspiratory transpulmonary pressure of < or = 15 cm H2O. In group 2(n = 6), tidal volume was adjusted to generate a transpulmonary pressure of 35 cm H2O and PEEP was set to 3 cm H2O. In group 3(n = 6), tidal volume was also adjusted to yield a transpulmonary pressure of 35 cm H2O but PEEP was set to 10 cm H2O. In each group, we instilled approximately 10(8) colony-forming units of E. coli into the trachea of the dogs and ventilated them with the chosen tidal volume and PEEP for 6 hrs afterward.

MEASUREMENTS AND MAIN RESULTS

We measured the pressure-volume relationship (pressure-volume curve) of the respiratory system before and 6 hrs after bacterial instillation. We obtained blood cultures before and 0.5, 1,2,3,4,5, and 6 hrs after bacterial instillation. After 6 hrs, the lungs were removed for histologic (histologic score) and gravimetric (wet-to-dry weight ratio, WW/DW) analysis. During the experiment 0, 5, and 1 dogs developed positive blood cultures in groups 1, 2, and 3, respectively. The number of dogs that developed bacteremia in group 2 was significantly greater than in the other two groups (p < .05). In group 1, pressure-volume curves demonstrated a lower inflection point which was greater than the end-inspiratory transpulmonary pressure suggesting that low transpulmonary pressure/low PEEP strategy ventilated aerated regions without expanding atelectatic areas. In group 2, pressure-volume curves demonstrated both a lower inflection point and an upper deflection point which were spanned by the tidal volume, suggesting that high transpulmonary pressure/low PEEP strategy might have caused both overdistention and cyclic closure and reopening. In group 3, pressure-volume curves demonstrated only a upper deflection point which was less than the maximal alveolar tidal pressure. At the end of the experimental protocol, group 2 manifested the most lung injury as assessed by gravimetric and histologic indices of lung injury. WW/DW of group 2(13.1 +/- 1.0 (SD); p < .05) was greater than groups 1 and 3(7.5 +/- 1.2 and 8.6 +/- 1.0, respectively). Similarly, the overall weighted histologic injury score for group 2 (1.19 +/- 0.26; p < .02) was greater than for groups 1 and 3 (0.82 +/- 0.20 and 0.88 +/- 0.22, respectively). For groups 2 and 3, the overall weighted histologic injury scores of the dependent regions were greater than the nondependent regions (p < .004).

CONCLUSIONS

We conclude that the ventilatory strategy most likely to overdistend the lungs while allowing repetitive opening and closure of alveoli (group 2) facilitated bacterial translocation from the alveoli to the bloodstream and increased lung injury, as determined by histologic and gravimetric analysis. PEEP ameliorated these effects, despite lung overdistention, but increased histologic and gravimetric indices of lung injury in dependent as compared with the nondependent regions.

Pathogenesis of bloodstream invasion with Haemophilus influenzae type b

Possible route(s) by which encapsulated bacteria invade the blood from the nasopharynx include (i) the direct invasion of submucosal blood vessels and (ii) clearance via lymphatics to regional nodes followed by bloodstream invasion. These possibilities were investigated in rats after intranasal inoculation with 10(5) Haemophilus influenzae type b. Within 24 h of inoculation, 10 of 42 rats with sterile blood cultures had similar numbers of H. influenzae b recovered from both cervical (local) and periiliac (distant) lymph nodes, which suggested early bacteremic spread. When virtually continuous blood cultures were obtained for 30 min after inoculation with 10(8) H. influenzae b, early transient bacteremia was documented in four of eight rats. Also, we found no significant difference in bacteremia among rats whose cervical lymph nodes had been removed surgically compared with sham-operated rats. These findings favor the hypothesis of a rapid, perhaps direct invasion of pharyngeal blood vessels as an initial determinant of the systemic spread of H. influenzae b.

Pathways of clearance in mouse lungs exposed to iron oxide aerosols

The history of particle clearance was studied in lungs of mice serially sacrificed at intervals up to 14 months following single exposures to an aerosol of submicronic, particulate, iron oxide used as a similitude for atmospheric dust. Clearance was followed by light microscopy in unstained and Prussian blue stained frozen and plastic embedded sections, as well as by electron microscopy, where iron oxide can be recognized by its form. Related problems were investigated through histochemical demonstration of acid phosphatase activity in pulmonary lysosomes and Prussian blue staining of various tissues after administration of iron compounds by gastrointestinal and vascular routes. The iron particles settle extensively but not uniformly on pulmonary alveolar surfaces. Clearance is centripetal and involves two mechanisms, an extracellular mechanism fed by fluid currents sweeping across the surfcace, and cellular mechanism principally involving alveolar macrophages. In the early post exposure period both actively remove deposited particles predominantly through the pulmonary airways. By 24 hours uncleared residues have become ingested and clearance thereafter results mainly from cellular action. Macrophages enter bronchial passages where they sometimes continue to pursue normal activities. A chronic phase of clearance begins when deposited particles become sequestered in macrophages of pulmonary connective tissues. These cells are reached by several routes, not least by crossing the bronchial epithelium. Particle clearance from these macrophages is very slow, and residue-containg cells eventually congregate in lymphoid tissues surrounding major bronchi. These findings are discussed as they help to develop an overall picture of clearance from the lungs and as they bear on related topics, such as functional roles of alveolar and pulmonary connective tissue macrophages and the pathogenesis of chronic bronchial disease.

An experimental analysis of the curative action of penicillin in acute bacterial infections. I. The relationship of bacterial growth rates to the antimicrobial effect of penicillin

Three strains of pneumococcus (types I and III), equally sensitive to penicillin, have been shown to be killed by the antibiotic in vitro when grown either in enriched beef infusion broth or in a thin serous exudate. Killing of the bacteria resulted promptly when the penicillin was added during the logarithmic phase of growth but failed to occur if addition of the antibiotic was delayed until the later "stationary" growth phase. In analogous experiments with thick purulent exudates from established subcutaneous abscesses, the pneumococci failed to grow rapidly, and added penicillin exerted only a relatively slow bactericidal effect. The relevance of these in vitro observations to the curative action of penicillin was demonstrated in a systematic histologic study of the antimicrobial effect of the drug in experimental (type I) pneumococcal pneumonia. Evidence was obtained that at least two distinct processes are involved. The first, the direct bactericidal effect of the penicillin itself, was shown to operate in the outer edema zone of the spreading pneumonic lesion where the micro-organisms multiply rapidly in the thin serous exudate. The second, which predominates in the older more central portions of the lesion, was demonstrated to depend upon destruction of the pneumococci by phagocytosis. Here the bacteria, having presumably reached a relatively stationary phase of growth in the alveolar exudate, are resistant to the bactericidal action of the penicillin but are readily destroyed by the phagocytes.

The nose in relation to the cerebrospinal fluid and lymph stream

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