Viral receptors

Brian Willett research

Investigations into the mechanism of infection with FIV have demonstrated that infection is mediated by an interaction between the virus and a molecule known as CXCR4, the receptor for the chemokine SDF-1.

Experiments performed in the Retrovirus Research Laboratory have demonstrated that FIV infection can be inhibited by SDF-1 and specific antagonists of CXCR4 raising the possibility of the use of such molecules as therapeutic agents in FIV infected cats. Thus it should be possible in the near future to treat FIV-infected cats with drugs that block the spread of the virus, preventing the development of feline AIDS.

Research highlights: viral receptors

The primary receptor for FIV

viral receptors

The initial event in the process of viral infection involves the binding of the virus to a molecule on the cell surface. Therefore, the expression pattern of this molecule within the host determines which cell types the virus will target. The receptor for human immunodeficiency virus (HIV) is CD4, a molecule that is expressed primarily on a specialised subset of cells within the immune system known as helper T cells (Th cells). Th cells play a pivotal role in the development of specific immune responses to pathogens and by targeting and destroying these cells selectively, HIV impairs the ability of the immune system to respond to infection. Consequently, HIV-infected individuals develop opportunistic infections and ultimately AIDS (acquired immune deficiency syndrome).

Although FIV targets Th cells, it has been known for several years that the virus does not use CD4 as a primary receptor. In a recent study, published in the journal Science, researchers from the Retrovirus Research Laboratory joined with colleagues in London and Japan to show that the primary receptor for FIV was a molecule known as CD134 (OX40).

What is CD134?

CD134

CD134 belongs to a large group of related molecules known as the nerve growth factor (NGF)/tumour necrosis factor (TNF) receptor superfamily. The molecule was first identified as "OX40", an antigen expressed on the surface of rat Th cells. It was subsequently found to be identical to an activation antigen found on human T cells known as "BerACT35".

The molecule functions in the development of antigen-specific T cell responses where it supports T cell expansion and survival by interacting with its ligand, CD134L (OX40L) on antigen presenting cells. Expression of feline CD134 expression on non-susceptible cells (eg human cells) renders the cells permissive for infection with FIV. Infection requires co-expression of a second molecule, CXCR4, a molecule we identified previously as the major co-receptor for FIV (see Nature 1997 J. Virology 1997).



Diagnostic tools

Monoclonal antibodies

Many of the antibodies generated in the Retrovirus Research Laboratory can be purchased from AbD Serotec Limited. The current list of reagents available is as follows:

Feline leucocyte differentiation antigens

Specificity  

Designation  

Catalogue number

Applications 

CD134 7D6 MCA2568 FC,WB
CD134-FITC 7D6 MCA2568F FC
CD134-A488 7D6 MCA2568A488 FC
CD134-A647 7D6 MCA2568A647 FC

CD4

vpg34

MCA1346 

FC, IP

CD4-FITC* 

vpg34

MCA1346F

FC

CD4 

vpg38

MCA1350

FC, IP

CD4

vpg39

MCA1349

FC, IP

CD8-RPE*

vpg9

MCA1347PE

FC

CD9

vpg15

MCA1345

FC, IP

MHC class II

vpg3

MCA1348

FC, IP

*CD4-FITC and CD8-RPE may be used for dual colour analysis of feline T cell subsets in a single tube format. The histograms below represent an analysis of T cell subsets in an FIV-infected cat using vpg34-FITC and vpg9-PE. Note the appearance of the "CD8low" sub-population (Immunology (1993), 78:1-6), a sub-population of CD8+ T cells thought to be CD8a  + b low (J Gen Virol. (1998), 79:91-94). This population is often observed in FIV infected cats.

Feline Immunodeficiency Virus

Specificity

Designation Catalogue number Applications
gp120 vpg68 MCA1351 IFA, FC, IP
p24 gag vpg50 MCA1353 IFA, IP, WB

Glutathione-S-Transferase

Specificity Designation

Catalogue number

Applications
GST vpg66 MCA1352 WB, IP
GST-biotinylated vpg66 MCA1352B WB, IP

vpg66 will recognise fusion proteins generated using the pGEX-2T vector and is ideal for both immunoprecipitation and western blot analyses. The use of vpg66 to detect fusion proteins between the HIV-1 Nef protein and GST is detailed in Harris, M. and Coates, K.C. (1993). J. Gen. Virol. 74, 1581-1589 and Harris, M.P.G. and Neil, J.C. (1994). J. Mol. Biol. 241, 136-142.

Additional antibodies against feline leukaemia virus, distinct epitopes on feline CD4, FIV p24 or FIV gp120 are available. Further information can be obtained from either the Retrovirus Research Laboratory or AbD Serotec.


Immunophenotyping

The Retrovirus Reseach Laboratory Flow Cytometry Service operates as an adjunct to routine haematology and is particularly useful where cases of leukaemia or lymphoma are suspected. Flow cytometry involves staining leukocytes from blood, effusions or aspirates with antibodies recognising cell surface markers that are specific for particular lineages of cells, for example T lymphocytes or B lymphocytes. The immunophenotype can be used to confirm that an expanded population of cells represents a malignant transformation rather than a reactive population responding to an infectious agent. In human medicine, an accurate diagnosis provides valuable prognostic and therapeutic information, particularly where chemotherapy is being attempted as is permits the accurate monitoring of the patient for the detection of minimal residual disease.

MGG staining Flow cytometry

The images show chronic lymphocytic leukaemia in a cat. A sample of peripheral blood was examined by flow cytometry. An aberrant population of B cell lineage (shown on the left) represented 85% of lymphocytes.

The Flow Cytometry Service will focus initially on feline and canine immunophenotyping. Samples should be submitted as EDTA anti-coagulated blood or body fluid.
For further information please contact Dr Brian J. Willett (0141 330 3274), or Mr Ronnie Barron (0141 330 6915) or e-mail us at the Retrovirus Research Laboratory).