 Surface proteins called Opa proteins can be used to bind to receptors on immune cells and prevent an immune response.At least 12 Opa proteins are known and the many permutations of surface proteins make recognizing "N. gonorrhoeae" and mounting a defense by immune cells more difficult.Lipooligosaccharide (LOS) is a low-weight version of lipopolysaccharide present on the surfaces of most other Gram-negative bacteria.