Immunoglobulin G antibodies directed against protein III block killing of serum-resistant Neisseria gonorrhoeae by immune serum.

Neisseria gonorrhoeae that resist complement-dependent killing by normal human serum (NHS) are sometimes killed by immune convalescent serum from patients recovering from disseminated gonococcal infection (DGI). In these studies, killing by immune serum was prevented or blocked by IgG isolated from NHS. Purified human IgG antibodies directed against gonococcal protein III, an antigenically conserved outer membrane protein, contained most of the blocking activity in IgG. Antibodies specific for gonococcal porin (protein I), the major outer membrane protein, displayed no blocking function. In separate experiments, immune convalescent DGI serum which did not exhibit bactericidal activity was restored to killing by selective depletion of protein III antibodies by immunoabsorption. These studies indicate that protein III antibodies in normal and immune human serum play a role in serum resistance of N. gonorrhoeae.

Conservation of the lipooligosaccharide synthesis locus lgt among strains of Neisseria gonorrhoeae: requirement for lgtE in synthesis of the 2C7 epitope and of the beta chain of strain 15253.

The present study was undertaken to examine the extent to which the lgt locus varies among strains of gonococci. This locus encodes five glycosyl transferases involved in the synthesis of the lipooligosaccharide (LOS) of Neisseria gonorrhoeae. We examined seven gonococcal strains and found that the structure of the lgt locus is conserved among six of these strains. The locus is strikingly altered in strain 15253. This is one of the few strains where extensive structural analysis of its LOS is available, and therefore, we defined the altered lgt locus and focused on the reactivity of mAB 2C7. We found that strain 15253 contains only two lgt genes, lgtA and lgtE. As in F62, lgtA encodes a GlcNAc transferase and is subject to phase variation. In addition, by analysis of deletion mutants, we found that lgtE, which encodes a galactosyl transferase that is required for elongating the alpha-chain, is also necessary for completing the beta chain.

Binding of complement factor H to loop 5 of porin protein 1A: a molecular mechanism of serum resistance of nonsialylated Neisseria gonorrhoeae.

Neisseria gonorrhoeae isolated from patients with disseminated infection are often of the porin (Por1A) serotype and resist killing by nonimmune normal human serum. The molecular basis of this resistance (termed stable serum resistance) in these strains has not been fully defined but is not related to sialylation of lipooligosaccharide. Here we demonstrate that Por1A bearing gonococcal strains bind more factor H, a critical downregulator of the alternative complement pathway, than their Por1B counterparts. This results in a sevenfold reduction in C3b, which is >75% converted to iC3b. Factor H binding to isogenic gonococcal strains that differed only in their porin serotype, confirmed that Por1A was the acceptor molecule for factor H. We identified a surface exposed region on the Por1A molecule that served as the binding site for factor H. We used gonococcal strains with hybrid Por1A/B molecules that differed in their surface exposed domains to localize the factor H binding site to loop 5 of Por1A. This was confirmed by inhibition of factor H binding using synthetic peptides corresponding to the putative exposed regions of the porin loops. The addition of Por1A loop 5 peptide in a serum bactericidal assay, which inhibited binding of factor H to the bacterial surface, permitted 50% killing of an otherwise completely serum resistant gonococcal strain. Collectively, these data provide a molecular basis to explain serum resistance of Por1A strains of N. gonorrhoeae.

A novel sialic acid binding site on factor H mediates serum resistance of sialylated Neisseria gonorrhoeae.

Factor H (fH), a key alternative complement pathway regulator, is a cofactor for factor I-mediated cleavage of C3b. fH consists of 20 short consensus repeat (SCR) domains. Sialic acid binding domains have previously been localized to fH SCRs 6-10 and 13. To examine fH binding on a sialylated microbial surface, we grew Neisseria gonorrhoeae in the presence of 5'-cytidinemonophospho-N-acetylneuraminic acid, which sialylates lipooligosaccharide and converts to serum resistance gonococci previously sensitive to nonimmune serum killing. fH domains necessary for binding sialylated gonococci were determined by incubating organisms with recombinant human fH (rH) and nine mutant rH molecules (deletions spanning the entire fH molecule). rH and all mutant rH molecules that contained SCRs 16-20 bound to the sialylated strain; no mutant molecule bound to serum-sensitive nonsialylated organisms. Sialic acid was demonstrated to be the fH target by flow cytometry that showed a fourfold increase in fH binding that was reversed by neuraminidase-mediated cleavage of sialic acid off gonococci. Functional specificity of fH was confirmed by decreased total C3 binding and almost complete conversion to iC3b on sialylated gonococci. Sialic acid can therefore bind fH uniquely through SCRs 16-20. This blocks complement pathway activation for N. gonorrhoeae at the level of C3.

Binding of C4b-binding protein to porin: a molecular mechanism of serum resistance of Neisseria gonorrhoeae.

We screened 29 strains of Neisseria gonorrhoeae and found 16/21 strains that resisted killing by normal human serum and 0/8 serum sensitive strains that bound the complement regulator, C4b-binding protein (C4bp). Microbial surface-bound C4bp demonstrated cofactor activity. We constructed gonococcal strains with hybrid porin (Por) molecules derived from each of the major serogroups (Por1A and Por1B) of N. gonorrhoeae, and showed that the loop 1 of Por1A is required for C4bp binding. Por1B loops 5 and 7 of serum-resistant gonococci together formed a negatively charged C4bp-binding domain. C4bp-Por1B interactions were ionic in nature (inhibited by high salt or by heparin), whereas the C4bp-Por1A bond was hydrophobic. Only recombinant C4bp mutant molecules containing the NH2-terminal alpha-chain short consensus repeat (SCR1) bound to both Por1A and Por1B gonococci, suggesting that SCR1 contained Por binding sites. C4bp alpha-chain monomers did not bind gonococci, indicating that the polymeric form of C4bp was required for binding. Using fAb fragments against C4bp SCR1, C4bp binding to Por1A and Por1B strains was inhibited in a complement-dependent serum bactericidal assay. This resulted in complete killing of these otherwise fully serum resistant strains in only 10% normal serum, underscoring the importance of C4bp in mediating gonococcal serum resistance.

Crystal structure at 3.5 A resolution of HIV-1 reverse transcriptase complexed with an inhibitor.

A 3.5 angstrom resolution electron density map of the HIV-1 reverse transcriptase heterodimer complexed with nevirapine, a drug with potential for treatment of AIDS, reveals an asymmetric dimer. The polymerase (pol) domain of the 66-kilodalton subunit has a large cleft analogous to that of the Klenow fragment of Escherichia coli DNA polymerase I. However, the 51-kilodalton subunit of identical sequence has no such cleft because the four subdomains of the pol domain occupy completely different relative positions. Two of the four pol subdomains appear to be structurally related to subdomains of the Klenow fragment, including one containing the catalytic site. The subdomain that appears likely to bind the template strand at the pol active site has a different structure in the two polymerases. Duplex A-form RNA-DNA hybrid can be model-built into the cleft that runs between the ribonuclease H and pol active sites. Nevirapine is almost completely buried in a pocket near but not overlapping with the pol active site. Residues whose mutation results in drug resistance have been approximately located.

Characterization of gonococcal antigens responsible for induction of bactericidal antibody in disseminated infection.

The role of gonococcal antigens in serum bactericidal activity was determined for an isolate of Neisseria gonorrhoeae from a patient with disseminated gonococcal infection (DGI). Gonococcal outer membranes were purified by differential ultracentrifugation of sheared organisms treated with EDTA. The membranes were solubilized in an endotoxin-disaggregating buffer, and the proteins were separated from the endotoxin by molecular sieve chromatography. Chemical characterization of the endotoxin from the DGI strain revealed the presence of heptose (7.8% of carbohydrate composition) and 2-keto-3-deoxyoctonate (6.1%, wt/wt) in concentrations similar to rough endotoxins of gram-negative enteric bacteria. Dermal Schwartzman reactions were positive for this endotoxin (4 mug) and the corresponding outer membrane (139 mug), but negative for the protein fraction (>500 mug). The patient's whole serum or the IgG fraction, each with complement, reduced the number of the infecting organisms by greater than 1 log(10) in a bactericidal assay. Outer membrane and its protein and endotoxin fractions (0.8-500 mug) from the DGI strain were separately preincubated with the patient's convalescent serum and specific inhibition of bactericidal activity occurred with the endotoxin fraction (25 mug) and the outer membrane (100 mug); the protein (500 mug) exhibited no inhibition. Similar results were obtained by inhibiting the bactericidal activity of rabbit antiserum, prepared by intravenous inoculation of an isolate from a patient with pelvic inflammatory disease, with antigen purified from that strain. That this was specific immune inhibition and not anticomplementary activity was shown by the failure of these antigens to inhibit other complement-dependent bactericidal systems.

Characterization of serum resistance of Neisseria gonorrhoeae that disseminate. Roles of blocking antibody and gonococcal outer membrane proteins.

Neisseria gonorrhoeae isolated from patients with disseminated infection (DGI) often resist complement (C')-dependent killing by normal human serum (NHS) and less commonly by convalescent DGI serum. 7 of 10 NHS specimens completely inhibited killing of serum-resistant (ser(r)) gonococci by convalescent or immune DGI serum. Immunoglobulin G (IgG) purified from NHS was shown to be the blocking agent. In addition, IgM (plus C') purified from NHS was shown to be fivefold more effective (wt/wt) in killing serum-sensitive (ser(s)) gonococci than equivalent amounts of IgM tested in the presence of IgG (whole serum). Although inhibition of NHS killing of ser(s) gonococci required a 640% excess of IgG, only a 40% excess was required to block immune serum killing of ser(r) gonococci. F(ab')(2) prepared from IgG also blocked killing of ser(r) gonococci by immune serum indicating antigenic specificity of blocking IgG.IgG immunoconcentrated against outer membrane protein (OMP) derived from ser(r) gonococci showed 40-fold increased blocking activity over normal IgG (wt/wt) and lacked antibody activity directed against gonococcal lipopolysaccharide by ELISA. Using direct immunoabsorption of IgG with purified gonococcal OMP; ser(r)-OMP was found sixfold more effective than ser(s)-OMP in neutralizing the blocking of immune serum killing of ser(r) gonococci, and 10-fold more effective in systems that used excess blocking IgG, NHS, and ser(s) gonococci. Blocking IgG preabsorbed with whole ser(r) gonococci lost 75% of its ability to block immune serum killing compared with no loss in this system using a similar absorption with ser(s) gonococci. IgG purified from NHS contained fivefold higher titers of antibody against ser(r)-OMP than ser(s)-OMP by ELISA.

Specificity of antibodies against Neisseria gonorrhoeae that stimulate neutrophil chemotaxis. Role of antibodies directed against lipooligosaccharides.

Five strains each of Neisseria gonorrhoeae sensitive or resistant to complement (C) dependent killing by normal human serum (NHS) were examined for their ability to stimulate chemotaxis of polymorphonuclear leukocytes (PMNs) after preincubation with NHS; or IgM or IgG derived from NHS. Serum-sensitive N. gonorrhoeae stimulated C-dependent chemotaxis when opsonized with IgM, but not IgG, however, serum-resistant strains, taken as a whole, failed to promote chemotaxis when opsonized with either isotype. IgM titers in NHS against lipooligosaccharide (LOS) antigens from individual serum-sensitive, but not serum-resistant strains, correlated with the magnitude of chemotaxis generated by the corresponding opsonized strains (r = 0.99). Western blots demonstrated that IgM and IgG from NHS recognized different antigenic determinants on LOS from serum-sensitive gonococci. IgM from NHS immunopurified against serum-sensitive LOS accounted for two-thirds of the chemotaxis promoting activity present in whole serum. IgG titers in NHS against LOS antigens from individual serum-resistant strains also correlated with magnitude of chemotaxis generated by the corresponding opsonized strains (r = 0.87), although most opsonized serum-resistant strains did not generate significantly higher magnitudes of chemotaxis than controls. In contrast, a serum-resistant isolate from a patient with disseminated gonococcal infection (DGI) stimulated chemotaxis when opsonized with IgG obtained from the patient's convalescent serum. By Western blot, convalescent IgG antibody recognized an additional determinant on serum-resistant LOS not seen by normal IgG.

Characterization of antigens from nontypable Haemophilus influenzae recognized by human bactericidal antibodies. Role of Haemophilus outer membrane proteins.

Major outer membrane antigens, proteins, and lipopolysaccharides (LPSs), from nontypable Haemophilus influenzae were characterized and examined as targets for complement-dependent human bactericidal antibodies. Outer membranes from two nontypable H. influenzae isolates that caused otitis media and pneumonia (middle ear and transtracheal aspirates) were prepared by shearing organisms in EDTA. These membranes were compared with membranes prepared independently by spheroplasting and lysozyme treatment of whole cells and found to have: similar sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of the proteins; identical densities (rho = 1.22 g/cm3); and minimal d-lactose dehydrogenase activity indicating purity from cytoplasmic membranes. Outer membranes were solubilized in an LPS-disaggregating buffer and proteins were separated from LPS by molecular sieve chromatography. The SDS-PAGE patterns of outer membrane proteins (OMPs) from the two strains differed in the major band although other prominent bands appeared similar in molecular weight. LPS prepared by hot phenol water extraction of each of the strains contained 45% (pneumonia isolate) and 60% (otitis isolate) lipid (wt/wt), 49% and 50% carbohydrate (wt/wt), respectively, and less than 1%, 3-deoxy-manno octulosonic acid. Immunoglobulin M (IgM) purified from normal human serum (NHS) plus complement was bactericidal for both strains. Purified immunoglobulin G (IgG) from NHS killed the middle ear isolate and immune convalescent IgM from the serum of the patient with pneumonia killed his isolate. NHS or convalescent serum were absorbed with OMPs and LPS (0.6-110 micrograms) from each of the strains and immune specific inhibition of bactericidal antibody activity by each antigen was determined. OMPs from the pulmonary isolate inhibited bactericidal antibody activity directed against the isolate in both NHS (1.5 microgram of antigen) and immune serum (0.75 microgram of antigen). OMPs (60 micrograms) from the ear isolate also inhibited bactericidal activity in the respective immune serum. LPSs exhibited minimal inhibition (greater than 110 micrograms). Three human sera (two normal, one immune) were selectively depleted of 80% of antibody activity against OMPs (measured by enzyme-linked immunosorbent assay) by affinity chromatography using OMPs from the pulmonary isolate coupled to a solid phase. These OMP antibody-depleted sera also showed an 88% reduction of bactericidal activity against this strain. Immunopurified antibody against OMPs eluted from the solid phase was bactericidal.

Identification of a 16,600-dalton outer membrane protein on nontypeable Haemophilus influenzae as a target for human serum bactericidal antibody.

A 16,600-D outer membrane protein is present in all strains of Haemophilus influenzae and antibodies to this protein are present in human serum. This study was designed to assess the role of this outer membrane protein (P6) in nontypeable H. influenzae as a target for human serum bactericidal antibody. P6 was isolated and coupled to an affinity column. Depleting normal human serum of antibodies to P6 by affinity chromatography resulted in reduced bactericidal activity of that serum for nontypeable H. influenzae. Immunopurified antibodies to P6 from human serum were bactericidal. Finally, preincubation of bacteria with a monoclonal antibody that recognizes a surface epitope on P6, inhibited human serum bactericidal killing. Taken together, these experiments establish that P6 is a target for human bactericidal antibodies. This observation provides evidence that P6 plays a potentially important role in human immunity to infection by nontypeable H. influenzae.

Mechanism of action of blocking immunoglobulin G for Neisseria gonorrhoeae.

Blocking immunoglobulin G (IgG) inhibits complement-mediated killing of serum-resistant Neisseria gonorrhoeae (GC) in immune human serum. We examined the mechanism of action of blocking IgG. Presensitization of GC with increasing concentrations of blocking IgG or F(ab')2 before incubation with bactericidal antibody and absorbed pooled normal human serum increased consumption and deposition of the third component of human complement (C3) and the ninth component of human complement (C9) but inhibited killing in dose-related fashion. We next showed that blocking IgG or F(ab')2 partially inhibited binding of bactericidal IgG to GC. Also, binding of a monoclonal antibody recognizing GC outer membrane protein PIII was almost completely inhibited by blocking F(ab')2, confirming other work (Rice, P. A., M. R. Tam, and M. S. Blake, manuscript submitted for publication) showing that PIII is a target for blocking antibody. Studies of the C3 deposition site showed that one quarter of the C3 deposited on GC in the presence of blocking IgG bound covalently to the antibody molecule. Finally, 125I-GC constituents with covalently bound C3 were affinity purified on Sepharose bearing antibodies to C3 and identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. C3 deposition on a 40,000-mol wt surface protein was enhanced six- to ninefold by blocking IgG, which indicates that the site of complement deposition was altered by blocking antibody. These studies show that blocking IgG competes with bactericidal antibody for binding to GC, but enhances rather than blocks complement activation, and leads to complement deposition at new sites that do not result in serum killing.

Making DNA do a U-turn: IHF and related proteins.

IHF and HU belong to a family of proteins that introduce sharp bends into DNA and act as accessory factors in a variety of cellular processes in prokaryotes. In addition to the crystal structure of IHF bound to DNA, the past year has seen a number of advances in the understanding of the interactions of these proteins with DNA in solution.

Refinement of gamma delta resolvase reveals a strikingly flexible molecule.

BACKGROUND: gamma delta resolvase is a 20.5 kDa enzyme that catalyzes a site-specific recombination in the second step of the transposition of the gamma delta transposon and requires no cofactors other than Mg2+ for activity. Dimers of resolvase bind cooperatively to DNA at three inverted repeat sequences of differing geometry but catalyze recombination at only one site. RESULTS: The structure of the catalytic domain of gamma delta resolvase, which provides the protein-protein interactions in the synaptic complex, has been refined to an R-factor of 20% at 2.3 A resolution. The structures of the three independent monomers in the asymmetric unit are similar but not identical. Differences occur in the positions of surface loops and in the overall twist of the central beta-sheet of the molecule. The crystal also gives two independent structures for the dimeric form of the molecule, which also show significant differences in the relative orientations of their subunits. CONCLUSION: Resolvase is an unusually flexible protein. This conformational adaptability may be necessary to allow each of the 12 resolvase subunits in the synaptic complex to play a different but specific role in wrapping DNA, binding sites of differing geometry and catalyzing recombination.

Pneumococcal bacteremia diagnosed by peripheral blood smear in multiple myeloma.

A patient with multiple myeloma and a normal spleen died with high-grade pneumococcal bacteremia diagnosed by routine examination of a Wright-stained peripheral blood smear. In earlier reports, this finding has been described only in patients with abnormal or absent spleens. We review the proposed mechanisms of high-grade pneumococcal bacteremia in these patients and the immunologic abnormalities in patients with multiple myeloma that may result in increased susceptibility to this infection.

The contrasting mechanisms of serum resistance of Neisseria gonorrhoeae and group B Neisseria meningitidis.

Neisseria gonorrhoeae and Neisseria meningitidis have evolved intricate mechanisms to evade complement-mediated killing. Sialylation of gonococcal lipooligosaccharide (LOS) results in conversion of previously serum sensitive strains to unstable serum resistance, which is mediated by factor H binding. Porin (Por) is also instrumental in mediating stable serum resistance in gonococci. The 5th loop of certain gonococcal PorlAs binds factor H, which efficiently inactivates C3b to iC3b. Factor H glycan residues may be essential for factor H binding to certain Por1A strains. Por1A strains can also regulate the classical pathway by binding to C4b-binding protein (C4bp) probably via the 1st loop of the Por molecule. Certain serum resistant Por1 B strains can also regulate complement by binding C4bp through a loop other than loop 1. Purified C4b can inhibit binding of C4bp to Por 1B, but not Por1A, suggesting different binding sites on C4bp for the two Por types. Unlike serum resistant gonococci, resistant meningococci have abundant C3b on their surface, which is only partially processed to iC3b. The main mechanism of complement evasion by group B meningococci is inhibition of membrane attack complex (MAC) insertion by their polysaccharide capsule. LOS structure may act in concert with capsule to prevent MAC insertion. Meningococcal strains with Class 3 Por preferentially bind factor H, suggesting Class 3 Por acts as a receptor for factor H.

Disseminated gonococcal infection: a prospective analysis of 49 patients and a review of pathophysiology and immune mechanisms.

Forty-nine patients with disseminated gonococcal infection (DGI) hospitalized at Boston City and University Hospitals over a 7-year period were studied. Patients with clinical manifestations of DGI and with cervical, urethral, rectal, pharyngeal, synovial or blood cultures positive for Neisseria gonorrhoeae were separated into two groups based on the presence or absence of suppurative arthritis. There were 19 cases of suppurative arthritis (Group II) and 30 cases with only tenosynovitis, skin lesions, or both (Group I). Blood cultures were positive only in Group I patients (43%) and synovial fluid cultures only in Group II patients (47%). Polyarthralgia was the most common initial symptom in both groups of patients. Twenty-six Group I patients had tenosynovitis (87%), while only 4 Group II patients (21%) had tenosynovitis (p less than 0.001). The knee was the most commonly involved suppurated joint. Twenty-seven Group I patients (90%) had skin lesions compared to 8 Group II patients (42%) (p less than 0.001). Some of these lesions progressed on treatment; some patients were unaware of their lesions. Genitourinary symptoms were unusual in both groups of patients. Eleven women (33%) were menstruating or were pregnant at the onset of DGI. Thirteen patients had histories suggestive of previous gonococcal infections; one had recurrent DGI. This patient and one other were found to have complement abnormalities. There were no cases of endocarditis or meningitis. Four patients had unexplained liver function abnormalities. All patients recovered uneventfully. Strains isolated from disseminated sites were predominantly of the transparent phenotype (90%). Many strains (58%) required arginine, hypoxanthine and uracil for growth. They were also more susceptible to penicillin than reported strains that cause pelvic inflammatory disease. Most strains were of a single outer membrane protein coagglutination serogroup, WI (85%). These characteristics did not vary between the Group I and Group II isolates. The two groups of strains, however, did vary in their complement-dependent bactericidal reactivity to normal human sera. Eighteen of 24 Group I strains (75%) versus 9 of 19 Group II strains (47%) resisted killing by all normal human sera tested (p less than .05). Likewise, convalescent sera from Group II patients were able to kill their infecting strains more often than did sera from Group I patients (70% vs 17%) (p less than 0.01). Thus, variations in the clinical expression of disease in patients with DGI may be explained, in part, by differences in certain phenotypic and immunologic features of infecting strains.

Salmonella heidelberg enteritis and bacteremia. An epidemic on two pediatric wards.

Symptomatic infection with Salmonella heidelberg developed in 55 children after their admission to the pediatric wards of two adjacent hospiatls in San Juan, Puerto Rico. Many of these children had been hospitalized for the treatment of diarrhea of unidentified etiology. In 25 of these patients, Salmonella bacteremia was documented. Five had clinically unsuspected and untreated bacteremia with no evidence of complications during the follow-up period of four and a half months. The remaining 30 had "standard" symptomatic infection due to S. heidelberg. Eight children died; four of these proved to be bacteremic. The index patient, who also introduced the infection into one of the hospitals, was identified. Person to person spread perpetuated the outbreak within and between the two hospitals for nearly four months. Although neonates with salmonellosis had a higher rate of bacteremia than other children, no other specific predisposing factors for Salmonella bacteremia were identified. Laboratory studies of the epidemic strain revealed neither invasive nor enterotoxic properties of the organisms, nor enhanced virulence in laboratory mice. Cohort nursing and isolation of patients with positive cultures halted the epidemic. Nontyphoid Salmonella bacteremia, sometimes clinically unsuspected and self-limited, should be recognized as a frequent accompaniment of Salmonella enteritis in young hospitalized children.

Pneumococcal pericarditis: a persisting problem in contemporary diagnosis.

We reviewed the clinical and laboratory features of six patients with pericarditis caused by Streptococcus pneumoniae who were admitted to Boston City Hospital. The diagnosis of pneumococcal pericarditis was delayed or missed entirely during life in all patients. The frequent absence of pericardial friction rubs and cardimegaly on chest roentgenograms contributed to the difficulty in recognizing this illness. Electrocardiograms and physical examinations of the heart almost always disclosed abnormalities, but they were not sufficiently specific to suggest pericarditis, and patients were often thought to have had an acute complication of arteriosclerotic heart disease. Review of the English literature since 1945 supports the recent experience in our hospital that the diagnosis of pneumococcal pericarditis may be elusive.

Chemical sympathectomy increases the innate immune response and decreases the specific immune response in the spleen to infection with Listeria monocytogenes.

Many investigators have shown that ablation of the sympathetic nervous system (SNS) with 6-hydroxydopamine (6-OHDA) can alter cell-mediated and humoral immune responses to antigenic challenge. Fewer studies have examined 6-OHDA-induced changes in natural immunity. In this study, we have examined the effect of chemical sympathectomy on the nonspecific and specific phases of the response to infection with Listeria monocytogenes. Sympathectomy decreased splenic bacterial loads 3 and 5 days post-infection and increased splenic neutrophils 3 days post-infection. Sympathectomy decreased splenocyte numbers and antigen-stimulated cytokine secretion from splenocytes. These results suggest that the SNS influences specific responses by modulating innate responses.