Mycobacterium leprae genomes from naturally infected nonhuman primates.

Leprosy is caused by the bacterial pathogens Mycobacterium leprae and Mycobacterium lepromatosis. Apart from humans, animals such as nine-banded armadillos in the Americas and red squirrels in the British Isles are naturally infected with M. leprae. Natural leprosy has also been reported in certain nonhuman primates, but it is not known whether these occurrences are due to incidental infections by human M. leprae strains or by M. leprae strains specific to nonhuman primates. In this study, complete M. leprae genomes from three naturally infected nonhuman primates (a chimpanzee from Sierra Leone, a sooty mangabey from West Africa, and a cynomolgus macaque from The Philippines) were sequenced. Phylogenetic analyses showed that the cynomolgus macaque M. leprae strain is most closely related to a human M. leprae strain from New Caledonia, whereas the chimpanzee and sooty mangabey M. leprae strains belong to a human M. leprae lineage commonly found in West Africa. Additionally, samples from ring-tailed lemurs from the Bezà Mahafaly Special Reserve, Madagascar, and chimpanzees from Ngogo, Kibale National Park, Uganda, were screened using quantitative PCR assays, to assess the prevalence of M. leprae in wild nonhuman primates. However, these samples did not show evidence of M. leprae infection. Overall, this study adds genomic data for nonhuman primate M. leprae strains to the existing M. leprae literature and finds that this pathogen can be transmitted from humans to nonhuman primates as well as between nonhuman primate species. While the prevalence of natural leprosy in nonhuman primates is likely low, nevertheless, future studies should continue to explore the prevalence of leprosy-causing pathogens in the wild.

Left Ventricular Hypertrophy in Rhesus Macaques (Macaca mulatta) at the California National Primate Research Center (1992-2014).

Necropsy records and associated clinical histories from the rhesus macaque colony at the California National Primate Research Center were reviewed to identify mortality related to cardiac abnormalities involving left ventricular hypertrophy (LVH). Over a 21-y period, 162 cases (female, 90; male, 72) of idiopathic LVH were identified. Macaques presented to necropsy with prominent concentric hypertrophy of the left ventricle associated with striking reduction of the ventricular lumen. Among all LVH cases, 74 macaques (female, 39; male, 35), mostly young adults, presented for spontaneous (sudden) death; more than 50% of these 74 cases were associated with a recent history of sedation or intraspecific aggression. The risk of sudden death in the 6- to 9-y-old age group was significantly higher in male macaques. Subtle histologic cardiac lesions included karyomegaly and increased cardiac myocyte diameter. Pedigree analyses based on rhesus macaque LVH probands suggested a strong genetic predisposition for the condition. In humans, hypertrophic cardiomyopathy (HCM) is defined by the presence of unexplained left ventricular hypertrophy, associated with diverse clinical outcomes ranging from asymptomatic disease to sudden death. Although the overall risk of disease complications such as sudden death, end-stage heart failure, and stroke is low (1% to 2%) in patients with HCM, the absolute risk can vary dramatically. Prima facie comparison of HCM and LVH suggest that further study may allow the development of spontaneously occurring LVH in rhesus macaques as a useful model of HCM, to better understand the pathogenesis of this remarkably heterogeneous disease.

Gene expression and TB pathogenesis in rhesus macaques: TR4, CD40, CD40L, FAS (CD95), and TNF are host genetic markers in peripheral blood mononuclear cells that are associated with severity of TB lesions.

Tuberculosis (TB) pathologic lesions in rhesus macaques resemble those in humans. The expression levels of several host TB candidate genes in the peripheral blood mononuclear cells (PBMCs) of six rhesus macaques experimentally infected with Mycobacterium tuberculosis were quantified pre-infection and at several dates post-infection. Quantitative measures of TB histopathology in the lungs including: granuloma count, granuloma size, volume of granulomatous and non-granulomatous lesions, and direct bacterial load, were used as the outcomes of a multi-level Bayesian regression model in which expression levels of host genes at various dates were used as predictors. The results indicate that the expression levels of TR4, CD40, CD40L, FAS (CD95) and TNF in PBMC were associated with quantitative measures of the severity of TB histopathologic lesions in the lungs of the study animals. Moreover, no reliable association between the expression levels of IFNE in PBMCs and the severity of TB lesions in the lungs of the study animals was found. In conclusion, PBMC expression profiles derived from the above-listed host genes might be appropriate biomarkers for probabilistic diagnosis and/or prognosis of TB severity in rhesus macaques.

Contribution of Endemic Listeriosis to Spontaneous Abortion and Stillbirth in a Large Outdoor-housed Colony of Rhesus Macaques (Macaca mulatta).

Listeria monocytogenes is an endemic agent in the primate population at the California National Primate Research Center and has been associated with both sporadic cases and a general outbreak of pregnancy failures. The primary objective of this study was to verify the incidence of L. monocytogenes-associated abortion and fetal deaths in the Center's outdoor breeding colony. In addition, we sought to compare the group of female macaques that presented with Listeria-associated abortion with both those with nonlisteria-associated abortion and animals with successful pregnancy outcome. We calculated the incidence of L. monocytogenes-associated abortion and stillbirth by dividing the number of positive L. monocytogenes cultures from aborted fetuses by the number of pregnant female macaques from 1989 through 2009. To compare the pregnancy outcome of female macaques that have presented L. monocytogenes-associated abortion and stillbirth, we created 2 control groups: female macaques with successful pregnancy outcomes during the 1999 breeding season and animals with nonlisteria-associated pregnancy failure. These macaques were followed for 2 subsequent breeding seasons. The results showed a range in the incidence of L. monocytogenes-associated abortion and stillbirth from 0% to 8.39% throughout the 1989 to 2009 breeding seasons. In addition, the Listeria-associated abortion group did not present statistically significant differences in fertility and abortion rates when compared with the control groups. We conclude that although L. monocytogenes is an endemic agent at the Center's outdoor breeding colony, the agent's incidence varied in significance. Furthermore, an episode of L. monocytogenes-associated abortion did not affect subsequent pregnancies.

Large scale pedigree analysis leads to evidence for founder effects of Hypertrophic Cardiomyopathy in Rhesus Macaques (Macaca mulatta).

Hypertrophic Cardiomyopathy (HCM) is the abnormal thickening of the ventricles and an increase in cardiac mass. Analyses of 108 rhesus macaque probands with pronounced HCM revealed a strong genetic predisposition to this disease. Macaques are ideal for investigating HCM because of their marked similarity to humans genetically, physiologically and anatomically.

Early mucosal sensing of SIV infection by paneth cells induces IL-1ß production and initiates gut epithelial disruption.

HIV causes rapid CD4+ T cell depletion in the gut mucosa, resulting in immune deficiency and defects in the intestinal epithelial barrier. Breakdown in gut barrier integrity is linked to chronic inflammation and disease progression. However, the early effects of HIV on the gut epithelium, prior to the CD4+ T cell depletion, are not known. Further, the impact of early viral infection on mucosal responses to pathogenic and commensal microbes has not been investigated. We utilized the SIV model of AIDS to assess the earliest host-virus interactions and mechanisms of inflammation and dysfunction in the gut, prior to CD4+ T cell depletion. An intestinal loop model was used to interrogate the effects of SIV infection on gut mucosal immune sensing and response to pathogens and commensal bacteria in vivo. At 2.5 days post-SIV infection, low viral loads were detected in peripheral blood and gut mucosa without CD4+ T cell loss. However, immunohistological analysis revealed the disruption of the gut epithelium manifested by decreased expression and mislocalization of tight junction proteins. Correlating with epithelial disruption was a significant induction of IL-1ß expression by Paneth cells, which were in close proximity to SIV-infected cells in the intestinal crypts. The IL-1ß response preceded the induction of the antiviral interferon response. Despite the disruption of the gut epithelium, no aberrant responses to pathogenic or commensal bacteria were observed. In fact, inoculation of commensal Lactobacillus plantarum in intestinal loops led to rapid anti-inflammatory response and epithelial tight junction repair in SIV infected macaques. Thus, intestinal Paneth cells are the earliest responders to viral infection and induce gut inflammation through IL-1ß signaling. Reversal of the IL-1ß induced gut epithelial damage by Lactobacillus plantarum suggests synergistic host-commensal interactions during early viral infection and identify these mechanisms as potential targets for therapeutic intervention.

Transcription profiling reveals potential mechanisms of dysbiosis in the oral microbiome of rhesus macaques with chronic untreated SIV infection.

A majority of individuals infected with human immunodeficiency virus (HIV) have inadequate access to antiretroviral therapy and ultimately develop debilitating oral infections that often correlate with disease progression. Due to the impracticalities of conducting host-microbe systems-based studies in HIV infected patients, we have evaluated the potential of simian immunodeficiency virus (SIV) infected rhesus macaques to serve as a non-human primate model for oral manifestations of HIV disease. We present the first description of the rhesus macaque oral microbiota and show that a mixture of human commensal bacteria and "macaque versions" of human commensals colonize the tongue dorsum and dental plaque. Our findings indicate that SIV infection results in chronic activation of antiviral and inflammatory responses in the tongue mucosa that may collectively lead to repression of epithelial development and impact the microbiome. In addition, we show that dysbiosis of the lingual microbiome in SIV infection is characterized by outgrowth of Gemella morbillorum that may result from impaired macrophage function. Finally, we provide evidence that the increased capacity of opportunistic pathogens (e.g. E. coli) to colonize the microbiome is associated with reduced production of antimicrobial peptides.

Metastatic hepatocellular carcinoma in a juvenile rhesus macaque (Macaca mulatta).

Neoplasia in juvenile (younger than 5 y) rhesus macaques has been estimated to represent only approximately 1.4% of all occurrences of spontaneous neoplasia. Here we report an unusual case of a 3.75-y-old primiparous female rhesus macaque that was euthanized due to poor prognosis associated with progressive anemia, marked hepatomegaly, and radiographic evidence of meta- static neoplasia. Postmortem examination revealed an invasive, hemorrhagic hepatic mass that effaced approximately 70% of the liver parenchyma and had evidence of metastatic spread to multiple abdominal organs, the lungs, and the pituitary gland. Neoplastic polygonal cells lined large necrohemorrhagic cavities and exhibited marked anisocytosis and anisokaryosis, with frequent multinucleate cells. There was no desmoplasia associated with the primary neoplasm or metastases. Immunohistochemical studies revealed the neoplastic cells to be diffusely reactive with pancytokeratin, cytokeratin 7, and cytokeratin 8/18 antibodies and rarely reactive with carcinoembryonic antigen antibodies. The cells did not react with vimentin, S100, CD31, or factor VIII antibodies. Tumor morphology and immunophenotype led to the diagnosis of anaplastic hepatocellular carcinoma. This report represents the first known case of metastatic liver neoplasia in a rhesus macaque. The young age of this animal and the aggressive nature of the neoplasm are highly unusual and reminiscent of adolescent onset hepatocellular carcinoma in humans.

Reference intervals for preprandial and postprandial serum bile acid in adult rhesus macaques (Macaca mulatta).

The purpose of this study was to determine the 12-h fasting preprandial and 2-h postprandial serum bile acid concentration (SBAC) reference intervals for healthy, adult rhesus macaques (Macaca mulatta). We hypothesized that the mean 2-h postprandial SBAC would be significantly higher than the mean preprandial SBAC. We included 40 (24 male, 16 female) macaques after confirming that their health records, physical examinations, CBC, serum chemistry panels, and urinalyses were all within normal limits. In addition, hepatitis A titers were determined, an ultrasound examination of the liver was performed, and two 16-gauge ultrasound guided percutaneous liver biopsies were collected and submitted for histopathology. Macaques were confirmed healthy according to hepatitis A screens and sonographic and histologic evaluation of hepatic tissue. Within 2 wk of the screening procedures, preprandial and postprandial SBACs were measured. Preprandial SBAC (mean ± 1 SD) was 11.1 ± 1.9 µmol/L and postprandial SBAC was 19.7 ± 8.0 µmol/L, which was significantly higher than the preprandial value. Sex and hepatitis titers did not significantly influence preprandial and postprandial SBAC. The current study indicates that the SBAC reference values for rhesus macaques are higher than those reported for humans and companion animals.

Meningoencephalitis due to Listeria monocytogenes in a pregnant rhesus macaque (Macaca mulatta).

We here report a spontaneous case of meningoencephalitis due to Listeria monocytogenes in an adult primiparous rhesus macaque (Macaca mulatta) during an outbreak of listeriosis in an outdoor enclosure. Clinical signs included tremors, abnormal posture, and altered mental status. Hematology and analyses of cerebrospinal fluid were consistent with bacterial infection. Pure cultures of L. monocytogenes were recovered from the placenta-abortus, cerebrospinal fluid, and brain tissue. The macaque did not respond to treatment and was euthanized. Histopathologic examination of the brain revealed acute meningoencephalitis. This case represents an unusual clinical and pathologic presentation of listeriosis in a nonhuman primate in which the dam and fetus both were affected.

Prolonged tenofovir treatment of macaques infected with K65R reverse transcriptase mutants of SIV results in the development of antiviral immune responses that control virus replication after drug withdrawal.

BACKGROUND: We reported previously that while prolonged tenofovir monotherapy of macaques infected with virulent simian immunodeficiency virus (SIV) resulted invariably in the emergence of viral mutants with reduced in vitro drug susceptibility and a K65R mutation in reverse transcriptase, some animals controlled virus replication for years. Transient CD8+ cell depletion or short-term tenofovir interruption within 1 to 5 years of treatment demonstrated that a combination of CD8+ cell-mediated immune responses and continued tenofovir therapy was required for sustained suppression of viremia. We report here follow-up data on 5 such animals that received tenofovir for 8 to 14 years. RESULTS: Although one animal had a gradual increase in viremia from 3 years onwards, the other 4 tenofovir-treated animals maintained undetectable viremia with occasional viral blips (≤ 300 RNA copies/ml plasma). When tenofovir was withdrawn after 8 to 10 years from three animals with undetectable viremia, the pattern of occasional episodes of low viremia (≤ 3600 RNA/ml plasma) continued throughout the 10-month follow-up period. These animals had low virus levels in lymphoid tissues, and evidence of multiple SIV-specific immune responses. CONCLUSION: Under certain conditions (i.e., prolonged antiviral therapy initiated early after infection; viral mutants with reduced drug susceptibility) a virus-host balance characterized by strong immunologic control of virus replication can be achieved. Although further research is needed to translate these findings into clinical applications, these observations provide hope for a functional cure of HIV infection via immunotherapeutic strategies that boost antiviral immunity and reduce the need for continuous antiretroviral therapy.

Evidence for an increased risk of transmission of simian immunodeficiency virus and malaria in a rhesus macaque coinfection model.

In sub-Saharan Africa, HIV-1 infection frequently occurs in the context of other coinfecting pathogens, most importantly, Mycobacterium tuberculosis and malaria parasites. The consequences are often devastating, resulting in enhanced morbidity and mortality. Due to the large number of confounding factors influencing pathogenesis in coinfected people, we sought to develop a nonhuman primate model of simian immunodeficiency virus (SIV)-malaria coinfection. In sub-Saharan Africa, Plasmodium falciparum is the most common malaria parasite and is responsible for most malaria-induced deaths. The simian malaria parasite Plasmodium fragile can induce clinical symptoms, including cerebral malaria in rhesus macaques, that resemble those of P. falciparum infection in humans. Thus, based on the well-characterized rhesus macaque model of SIV infection, this study reports the development of a novel rhesus macaque SIV-P. fragile coinfection model to study human HIV-P. falciparum coinfection. Using this model, we show that coinfection is associated with an increased, although transient, risk of both HIV and malaria transmission. Specifically, SIV-P. fragile coinfected macaques experienced an increase in SIV viremia that was temporarily associated with an increase in potential SIV target cells and systemic immune activation during acute parasitemia. Conversely, primary parasitemia in SIV-P. fragile coinfected animals resulted in higher gametocytemia that subsequently translated into higher oocyst development in mosquitoes. To our knowledge, this is the first animal model able to recapitulate the increased transmission risk of both HIV and malaria in coinfected humans. Therefore, this model could serve as an essential tool to elucidate distinct immunological, virological, and/or parasitological parameters underlying disease exacerbation in HIV-malaria coinfected people.

Stereological analysis of bacterial load and lung lesions in nonhuman primates (rhesus macaques) experimentally infected with Mycobacterium tuberculosis.

Infection with Mycobacterium tuberculosis primarily produces a multifocal distribution of pulmonary granulomas in which the pathogen resides. Accordingly, quantitative assessment of the bacterial load and pathology is a substantial challenge in tuberculosis. Such assessments are critical for studies of the pathogenesis and for the development of vaccines and drugs in animal models of experimental M. tuberculosis infection. Stereology enables unbiased quantitation of three-dimensional objects from two-dimensional sections and thus is suited to quantify histological lesions. We have developed a protocol for stereological analysis of the lung in rhesus macaques inoculated with a pathogenic clinical strain of M. tuberculosis (Erdman strain). These animals exhibit a pattern of infection and tuberculosis similar to that of naturally infected humans. Conditions were optimized for collecting lung samples in a nonbiased, random manner. Bacterial load in these samples was assessed by a standard plating assay, and granulomas were graded and enumerated microscopically. Stereological analysis provided quantitative data that supported a significant correlation between bacterial load and lung granulomas. Thus this stereological approach enables a quantitative, statistically valid analysis of the impact of M. tuberculosis infection in the lung and will serve as an essential tool for objectively comparing the efficacy of drugs and vaccines.

Cross-species transmission of a novel adenovirus associated with a fulminant pneumonia outbreak in a new world monkey colony.

Adenoviruses are DNA viruses that naturally infect many vertebrates, including humans and monkeys, and cause a wide range of clinical illnesses in humans. Infection from individual strains has conventionally been thought to be species-specific. Here we applied the Virochip, a pan-viral microarray, to identify a novel adenovirus (TMAdV, titi monkey adenovirus) as the cause of a deadly outbreak in a closed colony of New World monkeys (titi monkeys; Callicebus cupreus) at the California National Primate Research Center (CNPRC). Among 65 titi monkeys housed in a building, 23 (34%) developed upper respiratory symptoms that progressed to fulminant pneumonia and hepatitis, and 19 of 23 monkeys, or 83% of those infected, died or were humanely euthanized. Whole-genome sequencing of TMAdV revealed that this adenovirus is a new species and highly divergent, sharing <57% pairwise nucleotide identity with other adenoviruses. Cultivation of TMAdV was successful in a human A549 lung adenocarcinoma cell line, but not in primary or established monkey kidney cells. At the onset of the outbreak, the researcher in closest contact with the monkeys developed an acute respiratory illness, with symptoms persisting for 4 weeks, and had a convalescent serum sample seropositive for TMAdV. A clinically ill family member, despite having no contact with the CNPRC, also tested positive, and screening of a set of 81 random adult blood donors from the Western United States detected TMAdV-specific neutralizing antibodies in 2 individuals (2/81, or 2.5%). These findings raise the possibility of zoonotic infection by TMAdV and human-to-human transmission of the virus in the population. Given the unusually high case fatality rate from the outbreak (83%), it is unlikely that titi monkeys are the native host species for TMAdV, and the natural reservoir of the virus is still unknown. The discovery of TMAdV, a novel adenovirus with the capacity to infect both monkeys and humans, suggests that adenoviruses should be monitored closely as potential causes of cross-species outbreaks.

Social temperament and lymph node innervation.

Socially inhibited individuals show increased vulnerability to viral infections, and this has been linked to increased activity of the sympathetic nervous system (SNS). To determine whether structural alterations in SNS innervation of lymphoid tissue might contribute to these effects, we assayed the density of catecholaminergic nerve fibers in 13 lymph nodes from seven healthy adult rhesus macaques that showed stable individual differences in propensity to socially affiliate (Sociability). Tissues from Low Sociable animals showed a 2.8-fold greater density of catecholaminergic innervation relative to tissues from High Sociable animals, and this was associated with a 2.3-fold greater expression of nerve growth factor (NGF) mRNA, suggesting a molecular mechanism for observed differences. Low Sociable animals also showed alterations in lymph node expression of the immunoregulatory cytokine genes IFNG and IL4, and lower secondary IgG responses to tetanus vaccination. These findings are consistent with the hypothesis that structural differences in lymphoid tissue innervation might potentially contribute to relationships between social temperament and immunobiology.

Selected Background Findings and Interpretation of Common Lesions in the Female Reproductive System in Macaques.

The authors describe a selection of normal findings and common naturally occurring lesions in the reproductive system of female macaques, including changes in the ovaries, uterus, cervix, vagina, and mammary glands. Normal features of immature ovaries, uteri, and mammary glands are described. Common non-neoplastic lesions in the ovaries include cortical mineralization, polyovular follicles, cysts, ovarian surface epithelial hyperplasia, and ectopic ovarian tissue. Ovarian neoplasms include granulosa cell tumors, teratomas, and ovarian surface epithelial tumors. Common non-neoplastic uterine findings include loss of features of normal cyclicity, abnormal bleeding, adenomyosis, endometriosis, epithelial plaques, and pregnancy-associated vascular remodeling. Hyperplastic and neoplastic lesions of the uterus include endometrial polyps, leiomyomas, and rarely endometrial hyperplasia and endometrial adenocarcinoma. Vaginitis is common. Cervical lesions include endocervical squamous metaplasia, polyps, and papillomavirus-associated lesions. Lesions in the mammary gland are most often proliferative and range from ductal hyperplasia to invasive carcinoma. Challenges to interpretation include the normal or pathologic absence of menstrual cyclicity and the potential misinterpretation of sporadic lesions, such as epithelial plaques or papillomavirus-associated lesions. Interpretation of normal and pathologic findings is best accomplished with knowledge of the life stage, reproductive history, and hormonal status of the animal.

Effects of the macrolide drug tylosin on chronic diarrhea in rhesus macaques (Macaca mulatta).

Diarrhea is the gastrointestinal disease most frequently encountered in captive rhesus macaques. The precise pathogenic mechanisms underlying chronic diarrhea in nonhuman primates are not well understood, but a persistent inflammatory component has been implicated strongly. This study evaluated the inflammatory changes in the colon of macaques with diarrhea and assessed the efficacy of a 10-d course of tylosin in a cohort of 21 animals with chronic diarrhea. Stool quality was evaluated daily, and fecal consistency was scored. Colonoscopies were performed; biopsy samples were characterized histologically and assayed for expression of TNFalpha mRNA. Blood samples collected pre-, mid-, and post-treatment were assayed for C-reactive protein (CRP). The results indicated that 63% of the animals receiving tylosin showed improvement in stool quality, compared with 10% in the sham-treated group. Histologically, 82% of animals in the tylosin-treated group had a reduction in the severity of colonic lesions post-treatment, compared with 40% of animals in the sham group. The amount of TNFalpha mRNA before treatment did not differ from that afterward in either tylosin- or sham-treated animals. CRP levels serially decreased in tylosin-treated monkeys; the average post-treatment CRP value for tylosin-treated animals was 11.96 +/- 3.86 microg/ml compared with 26.48 +/- 4.86 microg/ml for sham-treated controls. In conclusion, tylosin significantly improved the fecal consistency score, significantly decreased colonic inflammation, and significantly decreased serum CRP levels post-treatment in rhesus macaques with chronic diarrhea.

SIV infection decreases sympathetic innervation of primate lymph nodes: the role of neurotrophins.

The sympathetic nervous system regulates immune responses in part through direct innervation of lymphoid organs. Recent data indicate that viral infections can alter the structure of lymph node innervation. To determine the molecular mechanisms underlying sympathetic denervation during Simian Immunodeficiency Virus (SIV) infection, we assessed the expression of neurotrophic factors and neuromodulatory cytokines within lymph nodes from experimentally infected rhesus macaques. Transcription of nerve growth factor (NGF), brain-derived neurotropic factor (BDNF) and neurotrophin-4 (NT4) decreased significantly in vivo during chronic SIV infection, whereas expression of the neuro-inhibitory cytokine interferon-gamma (IFN gamma) was up-regulated. Acute SIV infection of macaque leukocytes in vitro induced similar changes in the expression of neurotrophic and neuro-inhibitory factors, indicative of an innate immune response. Statistical mediation analyses of data from in vivo lymph node gene expression suggested that coordinated changes in expression of multiple neuromodulatory factors may contribute to SIV-induced depletion of catecholaminergic varicosities within lymphoid tissue. Given previous evidence that lymph node catecholaminergic varicosities can enhance SIV replication in vivo, these results are consistent with the hypothesis that reduced expression of neurotrophic factors during infection could constitute a neurobiological component of the innate immune response to viral infection.

Social stress enhances sympathetic innervation of primate lymph nodes: mechanisms and implications for viral pathogenesis.

Behavioral processes regulate immune system function in part via direct sympathetic innervation of lymphoid organs, but little is known about the factors that regulate the architecture of neural fibers in lymphoid tissues. In the present study, we find that experimentally imposed social stress can enhance the density of catecholaminergic neural fibers within axillary lymph nodes from adult rhesus macaques. This effect is linked to increased transcription of the key sympathetic neurotrophin nerve growth factor and occurs predominately in extrafollicular regions of the paracortex that contain T-lymphocytes and macrophages. Functional consequences of stress-induced increases in innervation density include reduced type I interferon response to viral infection and increased replication of the simian immunodeficiency virus. These data reveal a surprising degree of behaviorally induced plasticity in the structure of lymphoid innervation and define a novel pathway by which social factors can modulate immune response and viral pathogenesis.