(FIV) Feline Immunodeficiency Virus Blocking/Neutralizing Antibody Test

Hansen Dx is offering a new assay to measure the level of FIV Blocking/Neutralizing Antibodies in the serums of FIV infected cats. FIV is a Lentivirus which has one heavily glycosylated envelope protein in the viral membrane. The envelope protein is composed of two parts, the 95 KDA surface protein (SU), and the 36 KDA trans-membrane protein (TM). 

When FIV infects a cat, the virus targets the CD4 lymphocytes. Initially the virus binds with a primary cell surface receptor (CD-134). The binding causes a conformational change which exposes a secondary receptor, CXCR4. This second receptor facilitates the virus entry into the CD4 cell's interior. Antibodies directed against the parts of the virus that bind CXCR4 have the ability to block virus entry into the cell (1,2,5,&6). Antibodies directed against specific regions have been shown to be virus neutralizing in character (3,4,&7).

Our test measures antibodies in a FIV infected cat's serum that blocks the binding sites of both the virus and CD4+ cell surface, and then neutralizes the virus itself. We have tested over 500 naturally infected cats with our assay. Information on health status was available for us to evaluate. Of the infected cats, 23% had elevated levels of blocking/neutralizing antibodies against FIV. Of those cats, 85% were deemed clinically normal by the submitter. We believe that FIV positive cats that have and can maintain elevated levels of blocking/neutralizing antibodies are more likely to resist the onset of Immune Deficiency Syndrome and live a healthier life than FIV positive cats that are negative for those antibodies.

  1. Mapping of the CXCR4 binding site within variable region-3 of the Feline Immunodeficiency Virus surface glycoprotein. Journal of Virology, September 2008, Page 9134-9143. Sundstrom Et.Al.

  2. Selective interaction of heparin with the variable region-3 within surface glycoprotein of lab adapted Feline Immunodeficiency Virus plus one 9 (12); e115252.doi: 10.1371/journal.phone.0115252 Hu Et.Al.

  3. Feline Immunodeficiency Virus (FIV) Neutralization: A review of viruses. 2011 October; 3 (10): 1870-1890, Margaret J Hosie Et.Al.

  4. Unpublished data Inge DM Roukaerts; Gent University, Merelbeke, Belgium

  5. Feline definition of the CXCR4 binding region on the V3 loop of Feline Immunodeficiency Virus surface glycoprotein plus one 2010 5(5) e10689; Qion-Ying Hu, Et.Al.

  6. Replacement of V3 domain in the surface sub-unit of FIV envelope glycoprotein with T-cell Tropic HIV-I Results in efficient binding to CXCR4. AID Research Human Retroviruses ; 2014, March 1; 30(3): 250-259; Silvia Gonzalez, Et.Al.

  7. Improved Health and Survival of FIV-Infected Cats is associated with the presence of antibodies to the primary receptor, CD 134. PNAS, November 2009, Volume 106, No. 47, Page 19980-19985; Chris Grant.

About the Author


Herman Hansen, D.V.M. is the founder of Hansen Dx, and a recognized authority on Canine and Feline diagnostics. Dr. Hansen has authored many papers on the subject and has developed many important products over the years practice. His work was instrumental in the development of the assay to detect Feline Immunodeficiency Virus (FIV).