Cell membranes are also known as plasma membranes. Their structure surrounds every living cell and holds its contents inside. On the surface of membranes, there are antigens and proteins that are available for antibodies to bind against. Membranes can be permeable or semi-permeable which allows the flow of nutrients, fluids, wastes, and chemical messengers to be transported into and/ or out of the cell. In cells with nuclei, there is an internal nuclear membrane that is very similar in structure to the external cell membrane. Membranes are made of phospholipids, proteins and carbohydrates. The main structure is that of two phospholipid molecules arranged in separate layers with their fatty acid chains pointing towards each other creating a hydrophobic interior sandwiched between two hydrophilic phosphate layers. This is called the phospholipid bilayer. Secondary proteins form channels between the bilayer or peripheral surface proteins on the inner or outer membrane surface. These secondary proteins are surface molecules. Carbohydrates bind to these surface molecules in eukaryotic cell membranes forming even more complicated structures of most antigens. Surface molecules can exist on the surface (inner or outer) of the membrane itself and include transmembrane receptors, integrins, cadherins, and selectins.

Anti-FLVCR antibody binds against the target feline leukemia virus subgroup C cellular receptor. FLVCR functions as a heme transporter that exports cytoplasmic heme. Feline leukemia virus subgroup C cellular receptor also causes susceptibility to feline leukemia in vitro. FLVCR is localized in the cell membrane and specified in all hematopoietic tissues (including peripheral blood lymphocytes), pancreas, and kidney. FLVCR contains 555 amino acicds and 12 hydrophobic potential membrane-spanning sequences. Defects in feline leukemia virus subgroup C cellular receptor are the cause of posterior column ataxia with retinitis pigmentosa in humans and red cell erythroid aplasia (aplastic anemia) and feline leukemia virus in cats. Feline leukemia viruses are contagious infections in domestic cats that are proliferative, degenerative, and immunosuppressive. FelV type C is a mutant form of the FelV virus that occurs in about 1% of cats infected with feline leukemia and causes severe anemia. Symptoms of the feline leukemia virus include decreased immunity and progressive anemia. Many cats that come into contact with the virus (approx. 70%) will not develop the disorder because they will produce anti-FelV antibodies, like anti-flvcr antibody, and which will fight off the virus before the cat develops any symptoms. Red cell aplasia is a disorder of feline leukemia negative cats that is characterized by severe non-regenerative anemia and absence of erythroid cells in bone marrow. This disease is often fatal but can be treated with large amounts of immunosuppressive drugs over a long time period. Posterior column ataxia with retinitis pigmentosa is an autosomal recessive neurodegenerative disorder characterized by retinitis pigmentosa (an eye disease w/damage to the retina) and sensory ataxia (loss of coordination).