Role of viral strains and host genes in determining levels of immune complexes in a model system: implications for HIV infection

HIV-associated immune complex kidney disease

The introduction in the late 20(th) century of combination antiretroviral therapy (cART) to treat patients infected with HIV has changed the natural history of the disease from an acute illness that rapidly culminates in death, to a chronic condition that can be managed with medications. Over the past decade the epidemiology of kidney disease in US patients infected with HIV has changed, perhaps because of the increased availability and use of cART. Patients with HIV infection exhibit unique immunologic characteristics, including immunodeficiency and dysregulation of immunoglobulin synthetic responses and T-cell function, which can result in glomerular immune complex deposition and subsequent kidney injury. This Review examines the differential diagnoses of HIV-associated immune complex kidney diseases (HIVICD), and discusses the clinical manifestations and mechanisms underlying their development. We address the issues associated with treatment, clinical outcomes, and research needs to enhance our ability to diagnose and optimally treat patients with HIVICD.

Role of lymphocytic choriomeningitis virus (LCMV) in understanding viral immunology: past, present and future

Lymphocytic choriomeningitis virus (LCMV) is a common infection of rodents first identified over eighty years ago in St. Louis, MO, U.S.A. It is best known for its application in immunological studies. The history of LCMV closely correlates with the development of modern immunology. With the use of LCMV as a model pathogen several key concepts have emerged: Major Histocompatibility Complex (MHC) restriction, T cell memory, persistent infections, T cell exhaustion and the key role of immune pathology in disease. Given the phenomenal infrastructure within this field (e.g., defined immunodominant and subdominant epitopes to all T cell receptor specificities as well as the cognate tetramers for enumeration in vivo) the study of LCMV remains an active and productive platform for biological research across the globe to this day. Here we present a historical primer that highlights several breakthroughs since the discovery of LCMV. Next, we highlight current research in the field and conclude with our predictions for future directions in the remarkable field of LCMV research.

Travels along the viral-immunobiology highway

Michael Oldstone began his biomedical research career over three decades ago, showing contrary to established scientific dogma, the host was not tolerant but made a specific antiviral immune response during persistent virus infections. Further, the immune response to the virus actually caused tissue damage and disease, the first observation that several manifestations ordinarily accompanying infections were due to the host's antiviral immune response. These observations made originally with lymphocytic choriomeningitis virus (LCMV) and murine retroviruses were extended to other microbial infections including those in humans. Buildings on this work, he showed that antibodies to virus could recognize similar amino acid sequences or motifs found in host/cell proteins and cause disease. This cross-reactivity, referred to as molecular mimicry, has and is now been extensively studied by many laboratories. Another mechanism by which persistent virus infection produced disease was uncovered by cocumenting that viruses could alter the differentiation or "luxury" function of cells with causing cell destruction, thereby altering homeostasis. Finally, Oldstone was one of the first to show that viruses caused immunosuppression, abrogated immunologic surveillance resulting in viral persistence, work carried out long before HIV was discovered. He has also defined host-cell receptors for several viruses. In recent studies, host-cell receptor used by LCMV strains or variants that cause persistence have been identified. This led to observations that a single amino acid on the viral glycoprotein provides the infectious agent a selective ability ot displace extra-cellular matrix molecule, bind to and infect dendritic cells leading to their inability to act as antigen presenting cells thereby aborting the host's ability to generate the antiviral immune response required to clean the infection.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

Long-term antibody production is sustained by antibody-secreting cells in the bone marrow following acute viral infection

Acute viral infection of humans induces virus-specific serum antibody production that often persists for decades. To better understand the nature of this long-term antiviral antibody response, we studied antiviral antibody production of mice acutely infected with lymphocytic choriomeningitis virus (LCMV). Although this viral infection is resolved within 2 weeks, virus-specific serum antibody levels were maintained for > 300 days postinfection. The anatomic site of long-term antibody production was identified using an ELISPOT assay to quantitate LCMV-specific antibody-secreting cells (ASC). The initial antiviral ASC response in the spleen peaked at 8 days postinfection and then declined sharply, with less than 10% of the day 8 ASC population remaining after 60 days. Although no LCMV specific ASC were detected in the bone marrow at day 8, virus-specific ASC began accumulating in the bone marrow by 15 days postinfection. By day 60, approximately 10-fold more antiviral ASC were present in the bone marrow than in the spleen, and the bone marrow remained the major site of antibody production for > 10 months postinfection. To further characterize the LCMV-specific antibody response, the relative percentage of each IgG subclass (IgG1, IgG2a, IgG2b, and IgG3) was determined. IgG2a was the predominant IgG subclass produced during LCMV infection, and the IgG subclass profile of virus-specific ASC in the spleen and bone marrow matched the IgG subclass profile of virus-specific IgG in the serum. Following a secondary infection with LCMV, splenic ASC numbers increased rapidly with a peak at 5 days after secondary infection. This was followed by a sharp decline in ASC numbers by day 15. In contrast, virus-specific ASC numbers in bone marrow remained essentially unchanged during the acute phase of the secondary infection but increased approximately twofold at day 15, corresponding to a twofold increase in virus-specific serum antibody levels. These results indicate that following a primary viral infection or upon reexposure to a virus, the initial antibody response occurs in the spleen, but long-term antiviral antibody production is maintained in the bone marrow.

Competitive selection in vivo by a cell for one variant over another: implications for RNA virus quasispecies in vivo

Infidelity of genome applications of RNA viruses leads to the generation of viral quasispecies both in vitro and in vivo. However, the biological significance of such generated variants in vivo is largely unknown and controversial. To study this issue, we continued our evaluation of the tropism of a lymphocytic choriomeningitis virus (LCMV) variant termed clone 13 with its parental virus clonal pool ARM 53b (wild-type parent) for neuronal cells in vivo. Earlier in vivo and in vitro studies noted that the wild-type virus contained a Phe at glycoprotein (GP) residue 260 which correlated with neuron tropism compared with LCMV variants containing a Leu at residue 260 which showed selected tropism for cells of the immune system (C.F. Evans, P. Borrow, J. C. de la Torre, and M. B. A. Oldstone J. Virol. 68:7367-7373, 1994; L. Villarete, T. Somasundaram, and R. Ahmed, J. Virol 68:7490-7496, 1994). Here we (i) evaluated the ability of the viral variants with either a Phe or Leu at GP residue 260 to replicate in vivo in the spleen, liver, or brain, (ii) analyzed the ability of these viruses to compete against each other for cell (neuron)-specific selection following a single viral inoculation of different ratios of both viruses, and (iii) utilized genetic reassortants of both viruses to test their ability to replicate in neurons in vivo. We found that viral variants containing either a Phe or Leu at GP residue 260 were equally capable of replicating in neurons, but when inoculated together, neurons selected for the viral population containing Phe at GP residue 260 over viruses containing a Leu at this position. This was in contrast to selection in the liver and spleen that favored viruses with Leu and not Phe at GP residue 260. Analysis of inoculations with viral reassortants indicated that genes encoded on the short RNA (the GP and nucleoprotein, not the L [polymerase] and Z proteins that are encoded by the large RNA) were associated with neurotropism. Since the nucleoprotein sequences of wild-type Armstrong and clone 13 are identical, it is likely that specific cytoplasmic factors of the neurons play a fundamental role in the selection of virus with Phe at GP residue 260.

Bone marrow is a major site of long-term antibody production after acute viral infection

Antiviral antibody production is often sustained for long periods after resolution of an acute viral infection. Despite extensive documentation of this phenomenon, the mechanisms involved in maintaining long-term antibody production remain poorly defined. As a first step towards understanding the nature of long-term humoral immunity, we examined the anatomical location of antibody-producing cells during acute viral infection. Using the lymphocytic choriomeningitis virus (LCMV) model, we found that after resolution of the acute infection, when antiviral plasma cells in the spleen decline, a population of virus-specific plasma cells appears in the bone marrow and constitutes the major source of long-term antibody production. Following infection of adult mice, LCMV-specific antibody-secreting cells (ASC) peaked in the spleen at 8 days postinfection but were undetectable in the bone marrow at that time. The infection was essentially cleared by 15 days, and the ASC numbers in the spleen rapidly declined while an increasing population of LCMV-specific ASC began to appear in the bone marrow. Compared with the peak response at 8 days postinfection, time points from 30 days to more than 1 year later demonstrated greater-than-10-fold reductions in splenic ASC. In contrast, LCMV-specific plasma cell numbers in the bone marrow remained high and correlated with the high levels of antiviral serum antibody. The presence of LCMV-specific plasma cells in the bone marrow was not due to persistent infection at this site, since the virus was cleared from both the spleen and bone marrow with similar kinetics as determined by infectivity and PCR assays. The immunoglobulin G subclass profile of antibody-secreting cells derived from bone marrow and the spleen correlated with the immunoglobulin G subclass distribution of LCMV-specific antibody in the serum. Upon rechallenge with LCMV, the spleen exhibited a substantial increase in virus-specific plasma cell numbers during the early phase of the secondary response, followed by an equally sharp decline. Bone marrow ASC populations and LCMV-specific antibody levels in the serum did not change during the early phase of the reinfection, but both increased about two-fold by 15 days postchallenge. After both primary and secondary viral infections, LCMV-specific plasma cells were maintained in the bone marrow, showing that the bone marrow is a major site of long-term antibody production after acute viral infection. These results documenting long-term persistence of plasma cells in the bone marrow suggest a reexamination of our current notions regarding the half-life of plasma cells.

Analysis of envelope glycoprotein-specific antibodies from SIV-infected and gp110-immunized monkeys in ACC and ADCC assays

Sera collected from SIV-infected or recombinant glycoprotein-immunized monkeys were characterized for antibodies participating in antibody-complement-mediated cytolysis (ACC) and antibody-dependent cellular cytolysis (ADCC) in terms of their IgG subclass and epitope specificity. In a competitive inhibition ELISA, gp110-specific antibody reactivity with nondenatured rgp110 was blocked completely by soluble homologous rgp110 and partially inhibited by heterologous rgp110, suggesting cross-reactivity between viral strains. However, only partial inhibition was observed with denatured recombinant gp140 (rgp140) in selected monkeys, indicating that the majority of gp110-specific antibodies recognized conformational epitopes. ACC activity against recombinant vaccinia-infected, envelope-expressing targets was found in sera from both infected and immunized monkeys, whereas ADCC activity was observed only in sera from infected monkeys. ACC was blocked with denatured rgp140 as well as nondenatured rgp110, indicating that ACC-mediating antibodies recognized mainly linear epitopes. In contrast, rgp140 did not compete as effectively as rgp110 in the ADCC assay, indicating that the majority of ADCC antibodies recognized conformational epitopes. Competitive inhibition using three peptide fragments of gp110 indicated that epitopes recognized by ACC antibodies lie within amino acid residues 214-471, a region that spans V3, whereas ADCC-reactive epitopes lie between amino acid residues 52 and 214 at the N-terminal end of gp110. Column chromatography of rhesus IgG resulted in three subclass-enriched fractions, designated IgG-I, IgG-II, and IgG-III. IgG-I, but not IgG-II or IgG-III, from both infected and immunized monkeys mediated ACC, whereas IgG-I and IgG-II from infected monkeys mediated ADCC.(ABSTRACT TRUNCATED AT 250 WORDS)