Transmission of simian acquired immunodeficiency syndrome (SAIDS) with blood or filtered plasma

The US Military HIV Natural History Study: Informing Military HIV Care and Policy for Over 30 Years

INTRODUCTION

In October 1985, 4 years after the initial descriptions of the acquired immunodeficiency syndrome (AIDS), the U.S. Department of Defense (DoD) began routine screening for human immunodeficiency virus (HIV) infection to prevent infected recruits from exposure to live virus vaccines, implemented routine active-duty force screening to ensure timely care and help protect the walking blood bank, and initiated the U.S. Military HIV Natural History Study (NHS) to develop epidemiologic, clinical, and basic science evidence to inform military HIV policy and establish a repository of data and specimens for future research. Here, we have reviewed accomplishments of the NHS over the past 30 years and sought to describe relevant trends among NHS subjects over this time, with emphasis on combination antiretroviral therapy (cART) use and non-AIDS comorbidities.

METHODS

Subjects who were prospectively enrolled in the NHS from 1986 through 2015 were included in this analysis. Time periods were classified by decade of study conduct, 1986-1995, 1996-2005, and 2006-2015, which also correlate approximately with pre-, early-, and late-combination ART (cART) eras. Analyses included descriptive statistics and comparisons among decades. We also evaluated mean community log10 HIV viral load (CVL) and CD4 counts for each year.

RESULTS

A total of 5,758 subjects were enrolled between 1986 and 2015, of whom 92% were male with a median age of 28 years, and 45% were African-American, 42% Caucasian, and 13% Hispanic/other. The proportion of African-Americans remained stable over the decades (45%, 47%, and 42%, respectively), while the proportion of Hispanic/other increased (10%, 13%, and 24%, respectively). The CD4 count at HIV diagnosis has remained high (median 496 cells/uL), while the occurrence of AIDS-defining conditions (excluding low CD4 count) has decreased by decade (36.7%, 5.4%, and 2.9%, respectively). Following the introduction of effective cART in 1996, CVL declined through 2000 as use increased and then plateaued until guidelines changed. After 2004, cART use again increased and CVL declined further until 2012-15 when the vast majority of subjects achieved viral suppression. Non-AIDS comorbidities have remained common, with approximately half of subjects experiencing one or more new diagnoses overall and nearly half of subjects diagnosed between 2006 and 2015, in spite of their relatively young age, shorter median follow-up, and wide use of cART.

CONCLUSIONS

The US Military HIV NHS has been critical to understanding the impact of HIV infection among active-duty service members and military beneficiaries, as well as producing insights that are broadly relevant. In addition, the rich repository of NHS data and specimens serves as a resource to investigators in the DoD, NIH, and academic community, markedly increasing scientific yield and identifying novel associations. Looking forward, the NHS remains relevant to understanding host factor correlates of virologic and immunologic control, biologic pathways of HIV pathogenesis, causes and consequences of residual inflammation in spite of effective cART, identifying predictors of and potential approaches to mitigation of excess non-AIDS comorbidities, and helping to understand the latent reservoir.

Macrophages in Progressive Human Immunodeficiency Virus/Simian Immunodeficiency Virus Infections

The cells that are targeted by primate lentiviruses (HIV and simian immunodeficiency virus [SIV]) are of intense interest given the renewed effort to identify potential cures for HIV. These viruses have been reported to infect multiple cell lineages of hematopoietic origin, including all phenotypic and functional CD4 T cell subsets. The two most commonly reported cell types that become infected in vivo are memory CD4 T cells and tissue-resident macrophages. Though viral infection of CD4 T cells is routinely detected in both HIV-infected humans and SIV-infected Asian macaques, significant viral infection of macrophages is only routinely observed in animal models wherein CD4 T cells are almost entirely depleted. Here we review the roles of macrophages in lentiviral disease progression, the evidence that macrophages support viral replication in vivo, the animal models where macrophage-mediated replication of SIV is thought to occur, how the virus can interact with macrophages in vivo, pathologies thought to be attributed to viral replication within macrophages, how viral replication in macrophages might contribute to the asymptomatic phase of HIV/SIV infection, and whether macrophages represent a long-lived reservoir for the virus.

Fiber shaft-chimeric adenovirus vectors lacking the KKTK motif efficiently infect liver cells in vivo

The molecular mechanisms governing the infectivity of adenovirus (Ad) toward specific cell and tissue types in vivo remain poorly understood. The direct Ad binding to hepatic heparan sulfate proteoglycans via the KKTK motif within the fiber shaft domain was suggested to be the major mechanism of Ad liver cell infection in vivo. Here, we describe the generation and in vitro and in vivo infectivity studies of Ad5-based vectors possessing long Ad31- or Ad41-derived fiber shaft domains, which lack the KKTK motif. We found that all the critical early steps of Ad infection, including attachment to the cellular receptor, internalization, and virus genome transfer into the nucleus, occurred with similar levels of efficiency for fiber shaft-chimeric vectors and unmodified Ad5. Upon intravenous delivery into mice, fiber shaft-chimeric vectors accumulated in liver tissue, transduced liver cells, and induced the production of proinflammatory cytokines (tumor necrosis factor alpha and interleukin-6) and the chemokine monocyte chemoattractant protein 1 at levels indistinguishable from those observed for Ad5. Thus, our data provide evidence that the Ad5 fiber shaft amino acid sequence does not play any substantial role in determining adenovirus infectivity toward hepatic cells in vivo. The data obtained contribute to improving our understanding of the molecular mechanisms determining Ad infectivity and biodistribution in vivo and may aid in designing novel Ad-based vectors for gene therapy applications.

The history of simian AIDS

Retrospective data indicate that two separate outbreaks of simian AIDS and associated lymphoma were caused by Simian Immunodeficiency Virus (SIVmac and SIVstm, respectively) in group-housed macaques at the California Regional Primate Research Center (CRPRC) in the early and mid-1970s. Because these epizootics were not then recognized as infectious in nature, surviving healthy SIV carriers were sent to other primate centers where they transmitted the viruses to resident macaques. The source of SIV at the CRPRC was by contact with co-housed seropositive sooty mangabeys. Spread of SIV via saliva and blood while fighting most likely accounted for these epizootics. Separate outbreaks of a somewhat different version of simian AIDS, caused by the simian Type D retrovirus (SRV-1), and spread from healthy carriers via saliva and blood also occurred in the late 1970s and early 1980s in group-housed macaques at the CRPRC. Initially, these SRV-1 outbreaks were also not recognized as infectious.

Histopathological changes in lymph nodes of cats experimentally infected with the feline immunodeficiency virus (FIV)

Twelve specific-pathogen-free (SPF) kittens aged 8-12 weeks were serially infected in pairs every 6 weeks, by the intraperitoneal route, with the feline immunodeficiency virus (FIV). Three additional SPF kittens were kept as controls. The infected animals were killed 10 weeks after inoculation, during the primary phase of the FIV infection. Generalized lymphadenopathy (GL) was observed in the first three pairs of cats. All lymph nodes examined from the 12 infected cats showed histological changes. These included severe follicular hyperplasia with hyperactive follicular centres (FCs) which were either (1) naked, (2) infiltrated by lymphocytes, (3) seen to contain islets of lymphocytic mantle cells, or (4) disrupted by lymphocytes. The presence of both CD4+ and CD8+ T lymphocytes was demonstrated in the FCs immunocytochemically. The distribution of CD4 lymphocytes resembled that in control lymph nodes, but the CD8 cells were increased in number and either scattered or clustered in the follicles. In addition, varying degrees of interfollicular proliferation and medullary plasmacytosis were observed in the lymph nodes. These findings, which were common to all infected animals, represented distinct prodromal manifestations of FIV infection. The changes in lymphocyte subpopulation distribution observed in early FIV infection were reminiscent of findings encountered in human immunodeficiency virus (HIV) infection and reinforce the suggestion that FIV infection is an appropriate model for the study of HIV pathogenesis.

Characterization of T cell epitopes on the envelope glycoprotein of simian retrovirus 1 and 2 (SRV-1 and SRV-2) in several mouse strains

Various mouse strains were immunized with either SRV-1 or SRV-2 virus adsorbed on alum. Seven to 14 days later spleen cells were removed, and spleen cells were cultured with varying amounts of SRV-1 virus and SRV-2 virus, or varying amounts of selected SRV-1 and SRV-2 synthetic envelope peptides to determine their ability to initiate T cell proliferative responses. Our studies demonstrated that all mouse strains tested gave strong proliferative responses with SRV-2 virus. In contrast, SRV-1 virus induced T cell proliferative responses only in H-2k mouse strains. This apparent major histocompatibility complex (MHC)-restriction of SRV-1 virus-induced T cell proliferation correlates with the increased pathogenicity of SRV-1 virus in rhesus monkeys. The SRV envelope peptide 233-249 which is shared by both SRV-1 and SRV-2 virus initiates strong proliferative responses in both SRV-1 and SRV-2 virus immunized mice. The SRV-2 envelope peptide 96-102 initiates significant proliferative responses in SRV-2 immunized mice, and constitutes both a T and B cell epitope. The SRV-2 envelope peptide 127-152 has a 70% homology with the C-terminal region of SRV-1 peptide 142-167. The ability of SRV-2 peptide 127-152 to initiate T cell proliferation in SRV-1 virus immunized mice and the failure of the SRV-1 peptide 142-162 to initiate proliferation suggests that the region encompassing residues 160-167 must represent a T cell epitope in mice immunized with SRV-1 virus.

Immunobiological properties of a recombinant simian retrovirus-1 envelope protein and a neutralizing monoclonal antibody directed against it

We previously reported that an area encompassing amino acids 147-162 of the envelope region of the simian (type D) retrovirus serotype 1 (SRV-1) constitutes an antigenic site for the binding of murine and rhesus neutralizing antibodies. Neutralizing antibodies to SRV-2 are directed to a different area, encompassing residues 96-102 of SRV-2. This paper presents data on the activity of an SRV-1 recombinant envelope protein (rEP) and of monoclonal hybridoma cell line, C11B8, produced from murine spleen cells immunized with SRV-1 rEP. Purified monoclonal antibodies from C11B8 bind to the SRV-1 rEP and to both SRV-1 and SRV-2. However, the monoclonal antibody exhibits strain specificity in the capacity to neutralize SRV-1 infection in vitro. Thus, C11B8 neutralizes SRV-1 infection but fails to neutralize four other known serotypes of the virus. C11B8 also binds to an SRV-1 synthetic peptide representing residues 142-167, which encompasses the previously defined antigenic site of recognition for neutralizing antibodies to SRV-1. This paper also contains evidence that the SRV-1 rEP construct binds the site for SRV-1 attachment to the cell receptor. This is indicated by the ability of SRV-1 rEP to compete with SRV-1 (but not with SRV-2) and inhibit its infectivity in vitro. In addition, SRV-1 rEP inhibits the neutralizing activity of C11B8 against SRV-1 infection in vitro. SRV-1 rEP has no inhibitory effect on rhesus neutralizing antibodies to SRV-2. Taken together, the above findings indicate that immunity conferred at the level of neutralizing antibodies during SRV infection is strain-specific and involves the recognition of envelope sequences unique to each strain.

Synthetic peptides of envelope proteins of two different strains of simian AIDS retrovirus (SRV-1 and SRV-2) represent unique antigenic determinants for serum neutralizing antibodies

There are at least three distinct serotypes of simian type D retrovirus (SRV) which exhibit extensive serological cross-reactivity, but no cross-reactivity exists at the level of serum neutralizing antibodies. Amino acid sequence analysis and hydrophobicity plots of SRV-1 and SRV-2 envelope proteins were compared in order to identify unique potential antigenic determinants to which respective neutralizing antibodies may be directed. Peptides representing residues 147-162 of SRV-1 and 96-102 of SRV-2 were synthesized and assessed for their immunoreactivity. Free peptide inhibition of strain-specific serum (rhesus) neutralizing antibodies to SRV-1 and SRV-2 was demonstrated using the SRV-1 147-162 peptide and the SRV-2 peptide, 96-102, respectively. Inhibition of serum neutralizing activity by these peptides was also strain-specific, showing no cross-inhibition. SRV-1 147-162 conjugated to a protein carrier and cross-linked to Sepharose beads specifically adsorbed neutralizing antibodies from SRV-1 immune rhesus sera. The antibodies eluted from the immunoadsorbent possessed SRV-1 neutralizing activity, but showed no effect on the infectivity of SRV-2. Peptide SRV-1 147-162 also exhibited the capacity to bind specifically with a mouse monoclonal antibody which neutralizes the infectivity of SRV-1. Mice immunized with a recombinant SRV-1 envelope protein or with whole, inactivated SRV-1 produced antibodies which bound the SRV-1 147-162 conjugate, but not the protein carrier itself. Mouse antibodies to the SRV-1 147-162 conjugate exhibited specific binding with both native SRV-1 and with recombinant SRV-1 envelope protein. These findings provide strong evidence that SRV-1 147-162 and SRV-2 96-102 constitute at least two unique antigenic determinants, or parts thereof, which participate in the strain-specific neutralizing antibody response. Moreover, the findings indicate that the SRV-1 neutralizing antibodies produced by monkeys and at least a certain population of neutralizing antibodies produced by mice recognize the same epitope of SRV-1.

Sustained increases in cerebrospinal fluid quinolinic acid concentrations in rhesus macaques (Macaca mulatta) naturally infected with simian retrovirus type-D

Sustained increases in CSF concentrations of the excitotoxin quinolinic acid (QUIN) occur in patients with AIDS and have been implicated in the pathogenesis of the AIDS dementia complex. Macaques in captivity may also develop immunodeficiency syndromes caused by retrovirus infection, including simian retrovirus type-D. In the present study, CSF QUIN concentrations were moderately increased in retrovirus type-D-positive/antibody-negative macaques (163.8 +/- 35.1 nmol/l; P less than 0.0001, n = 21) but not virus-negative/antibody-positive macaques (27.4 +/- 9.4 nmol/l, n = 8) compared to uninfected control macaques (23.0 +/- 1.6 nmol/l; n = 22). CSF QUIN concentrations in virus-positive/antibody-negative macaques tended to remain elevated over a 4-20 month period. Post-mortem studies of 9 virus-positive/antibody-negative macaques and 6 virus-negative/antibody-positive macaques revealed inflammatory responses in the brains of 6 of 9 virus-positive/antibody negative macaques, including lymphocytic infiltrates of the choroid plexus in 3 macaques, glial nodules in 3 macaques and perivascular infiltrates in 1 macaque. These lesions were not extensive and no evidence of brain atrophy was observed. No lesions were observed in the 6 antibody-positive/virus-negative macaques. Small increases in plasma L-kynurenine in virus-positive/antibody-negative macaques are consistent with activation of indoleamine-2,3-dioxygenase, the first enzyme in the kynurenine pathway. We conclude that sustained moderate increases in CSF QUIN occur in viremic simian retrovirus type-D macaques. The increases in CSF QUIN may reflect inflammatory responses within the brain or synthesis of QUIN precursors in systemic tissues, their entry into brain and subsequent conversion to QUIN. The neuropathologic significance of these increases in CSF QUIN remains to be determined.

Tropical spastic paraparesis: clinical, immunological, and virological studies in two patients from Martinique

Two patients from Martinique with tropical spastic paraparesis had antibodies to human T-lymphotropic virus type I (HTLV-I) in serum and spinal fluid but no antibodies to other retroviruses tested. They presented with spastic weakness of both lower extremities, hyperreflexia with upgoing toes, sphincteric dysfunction, and normal sensation. By means of agarose isoelectric focusing and selective immunoblotting we demonstrated an increased intrathecal synthesis of IgG antibodies to HTLV-I in the spinal fluid. Unique oligoclonal bands of IgG antibodies to HTLV-I were present in the cerebrospinal fluid. Using a battery of monoclonal antibodies we also found in these patients an increased number of circulating T cells that expressed activation markers. We conclude that the HTLV-I retrovirus associated with tropical spastic paraparesis has both lymphocytotropic and neurotropic properties.

Induction of simian acquired immune deficiency syndrome (SAIDS) with a molecular clone of a type D SAIDS retrovirus

We have isolated a molecular clone of the full-length integrated provirus of simian acquired immune deficiency syndrome retrovirus serotype 1 (SRV-1) from a fatal case of simian acquired immune deficiency syndrome in a juvenile rhesus macaque. An integrated SRV-1 provirus was cloned, sequenced, and found to contain four large open reading frames encoding gag-precursor protein, protease, polymerase, and envelope. The proviral clone was transfected into D17 canine osteosarcoma cells and found to produce infectious virus. A comparison of the sequences of this clone with a noninfectious clone showed 20 differences, resulting in 10 amino acid changes. Also, a cluster of exchanges, short insertions, and deletions in the 5' leader sequences resulted in extension of the tRNA(Lys) primer-binding site from 14 to 19 nucleotides. Virus isolated from transfected cells was shown to be infectious and pathogenic, resulting in disease that followed the same time course and mortality as disease induced by uncloned, in vitro cultivated virus isolated from diseased animals. These results unequivocally show that a type D retrovirus (SRV-1) causes a fatal immunosuppressive syndrome in rhesus monkeys.

Functional interaction and partial homology between human immunodeficiency virus and neuroleukin

Dementia is common in patients with AIDS, but the mechanism by which the human immunodeficiency virus type 1 (HIV-1) causes the neurological impairment is unknown. In this study the possibility that an antigen of HIV-1 suppresses neuronal responses to neurotrophic factors was examined. Both HIV-1 and a related retrovirus, simian immunodeficiency virus (SIV), inhibited the growth of sensory neurons from chick dorsal root ganglia in medium containing neuroleukin (NLK) but not in medium containing nerve growth factor. An unrelated type D retrovirus, simian acquired immunodeficiency syndrome virus, did not affect the growth of neurons in the presence of either neurotrophic factor. The inhibition by HIV-1 of neuron growth in the presence of NLK was found to be due to the gp120 envelope glycoprotein. Regions of sequence homology between gp120 and NLK may account for this inhibitory property of gp120 and functional interactions between gp120 and NLK may be important in the pathogenesis of the AIDS dementia complex.

An immunopathologic evaluation of lymph nodes from monkey and man with acquired immune deficiency syndrome and related conditions

Morphology and immunostaining of lymph nodes taken from rhesus monkeys and man are compared. The monkeys were inoculated with biologic materials known to transmit simian acquired immune deficiency syndrome (SAIDS) and the human biopsies were obtained from homosexual men with persistent generalized lymphadenopathy syndrome or acquired immune deficiency syndrome (AIDS). The lymph nodes from monkey and man share common immunohistochemical features, ranging from exhuberant follicular hyperplasia to lymphocyte depletion stage. The follicular hyperplasia differed from reactive controls by the larger follicular size and disorganization within the follicular centers as well as an increase in the number of cells with the T suppressor/cytotoxic phenotype. The lymphocyte depletion stage showed a loss of reactive follicles and small T lymphocytes with a predominance of mature monocytes/macrophages. Most monkeys and humans with the lymphocyte depletion morphology fulfilled the case definitions for AIDS and SAIDS while those with follicular hyperplasia usually had 'prodromal' findings. The simian agent is associated with alterations in lymph node morphology and immunostaining which parallel the changes seen in spontaneous human cases supporting a similar pathogenesis for AIDS and SAIDS.

Virus-associated deficiencies in the mitogen reactivity in celebes black macaques (Macaca nigra)

Celebes black macaques (Macaca nigra) with a history of diabetes mellitus, recurrent bacterial and protozoal infections, diarrhea, anemia, weight loss, anorexia, and a high mortality were studied to determine their immune status. Two groups of monkeys, healthy and unhealthy, were formed on the basis of a clinical assessment. The proliferative response and the pokeweed-mitogen-induced polyclonal IgG response of peripheral blood mononuclear cells of unhealthy monkeys were significantly less than the responses of healthy monkeys. The percentage of HLA-DR+ cells varied greatly in unhealthy monkeys. The OKT4/OKT8 ratios of unhealthy monkeys were generally greater than the ratios of healthy monkeys. Unhealthy monkeys usually had smaller percentages of OKT8+ cells than did healthy monkeys. The two groups of monkeys were examined for the presence of a syncytial forming retrovirus by a coculture assay involving Raji cells, a human B lymphoblastoid cell line. A type D retrovirus was detected in the unhealthy group but not in the healthy group. Retroperitoneal fibromatosis was detected in several monkeys in the unhealthy group.

Neurological manifestations of the acquired immunodeficiency syndrome (AIDS): experience at UCSF and review of the literature

In this review of the acquired immunodeficiency syndrome (AIDS), the authors have evaluated a total of 352 homosexual patients with AIDS or generalized lymphadenopathy managed at the University of California, San Francisco (UCSF), between 1979 and 1984. Of an initial unselected group of 318 patients, 124 (39%) were neurologically symptomatic, and one-third already had their neurological complaints at the time of presentation. An additional 210 AIDS patients with neurological symptoms have been reported in the literature. Thus, a total of 366 neurologically symptomatic patients with AIDS or lymphadenopathy are reviewed. Central nervous system (CNS) complications, encountered in 315 patients, included the following viral syndromes: subacute encephalitis (54), atypical aseptic meningitis (21), herpes simplex encephalitis (nine), progressive multifocal leukoencephalopathy (six), viral myelitis (three), and varicella-zoster encephalitis (one). Non-viral infections were caused by Toxoplasma gondii (103), Cryptococcus neoformans (41), Candida albicans (six), Mycobacteria (six), Treponema pallidum (two), coccidioidomycosis (one), Mycobacterium tuberculosis (one), Aspergillus fumigatus (one), and Escherichia coli (one). Neoplasms included primary CNS lymphoma (15), systemic lymphoma with CNS involvement (12), and metastatic Kaposi's sarcoma (three). Cerebrovascular complications were seen in four patients with hemorrhage and five with infarction. Five patients in the UCSF series had multiple intracranial pathologies, including two cases of simultaneous Toxoplasma gondii infections and primary CNS lymphoma, two cases of coexistent Toxoplasma gondii and viral infections, and one case of combined Toxoplasma gondii and atypical mycobacterial infection. Cranial or peripheral nerve complications, seen in 51 patients, included cranial nerve syndromes secondary to chronic inflammatory polyneuropathy (five), lymphoma (five), and Bell's palsy (five). Peripheral nerve syndromes included chronic inflammatory polyneuropathy (12), distal symmetrical neuropathy (13), herpes zoster radiculitis (six), persistent myalgias (two), myopathy (two), and polymyositis (one). In light of the protean behavior of AIDS and the problems related to the clinical, radiological, and serological diagnosis of the unusual and varied associated nervous system diseases, patients with AIDS and neurological complaints require a rigorous and detailed evaluation. The authors' experience suggests that biopsy of all CNS space-occupying lesions should be performed for tissue diagnosis prior to the institution of other therapies.

Immune defects in simian acquired immunodeficiency syndrome

We recently reported a Simian Acquired Immunodeficiency Syndrome (SAIDS) in rhesus macaques at the California Primate Research Center. Here, we studied in vitro lymphocyte response to the mitogens Concanavalin A (Con A), phytohemagglutinin (PHA) and pokeweed mitogen (PWM) with and without interleukin 2 (IL-2). Immunoglobulin (IgG and IgM) and complement (C3 and C4) concentrations were determined by radial immunodiffusion. T helper and T suppressor lymphocytes were identified with the monoclonal antibodies OKT4 and OKT8. Concentrations of IgG and IgM were significantly (p less than .05) decreased. Complement component C3 did not change but C4 was increased. The absolute lymphocyte count decreased but the OKT4:OKT8 ratio was unchanged from controls. A decreased lymphocyte response to all mitogens occurred early and became more severely depressed near death. IL-2 caused a complete or partial restoration of the response to the mitogens CON A and PHA. Both the humoral and cell mediated immune responses are affected in SAIDS. The role of IL-2 in this immune defect must be studied further.

Simian AIDS--evidence for a retroviral etiology

This paper reviews the major features of a simian model of acquired immunodeficiency ('SAIDS'), SAIDS occurs endemically in colonies of macaque monkeys in the United States and resembles AIDS in humans in overall clinical manifestations, pathology, and immune deficiency. An infectious type D retrovirus, related to but distinct from the Mason-Pfizer monkey virus, has been identified as the primary cause of SAIDS. The relevance of these findings for human AIDS is discussed.

Unregulated production of virus and/or sperm specific anti-idiotypic antibodies as a cause of AIDS

A network of idiotypic and anti-idiotypic antibodies is often suggested as the basis for cellular interactions that maintain a steady-state immunological equilibrium. This hypothesis proposes that repeated exposure to certain external antigens--ie, both viral and sperm--stimulates an unregulated production of a uniquely potent immunomodulating idiotypic antibody(ies). In a genetically predisposed individual, this particular antibody(ies), which is also an autoantibody(ies), results in a cellular immune deficiency. This disruption in the immune system permits opportunistic infection and thus the acquired immune deficiency syndrome. This hypothesis, which is readily testable and which does not involve a primary pathogen, can explain both the active induction of this disease in, as well as its passive transfer to, all at-risk populations.

Simian AIDS: isolation of a type D retrovirus and transmission of the disease

A type D retrovirus related to but distinct from Mason-Pfizer monkey virus was isolated in vitro from the blood of two rhesus monkeys (Macaca mulatta) with simian acquired immunodeficiency syndrome (SAIDS). Three juvenile rhesus monkeys that were injected intravenously with tissue culture fluids containing this virus developed SAIDS after 2 to 4 weeks.