Which property is not exhibited by HLA molecules?

• A. They belong to the immunoglobulin superfamily
• B. They are heterodimeric
• C. They are integral cell membrane glycoproteins
• D. They are monomorphic

Answer: (D)

HLA molecules are part of the major histocompatibility complex and are membrane glycoproteins with immunoglobulin-like domains, which is why they’re said to belong to the immunoglobulin superfamily. They function as heterodimers: class I molecules have a heavy chain associated with beta-2 microglobulin, while class II molecules consist of alpha and beta chains that pair together. They are integral membrane proteins, spanning the cell membrane and carrying glycosylations. They are not monomorphic; in contrast, HLA genes are highly polymorphic with many alleles in the population, enabling a broad range of peptide presentation to T cells.