What are the properties of antigens?

Antigens are typically large molecules with high molecular weight (14,000-6,00,000 Da), often consisting of polysaccharides or proteins. Additionally, molecules such as lipids and nucleic acids can serve as antigens when they form complexes with proteins and polysaccharides. They have the ability to trigger an immune response by stimulating the production of antibodies or activating immune cells such as T cells and B cells. Antigens are typically considered immunogenic when they have a molecular weight greater than 5000 Da. However, even low molecular weight substances can become immunogenic when they are attached to larger carrier molecules. The greater the chemical complexity of antigens, the stronger their ability to induce an immune response. Rigid molecules tend to be better antigens because they can elicit antibodies against specific structures more effectively than less rigid ones. Another property is that antigenic determinants are specific regions within an antigen molecule that interact with antibodies. Typically, antigens containing two or more antigenic determinants can stimulate the production of antibodies. Therefore, smaller antigens often fail to induce antibody production because they lack multiple antigenic determinants. Cross-reactivity is another crucial factor, where antibodies generated in response to one antigen can interact with a different antigen. Lastly, the immune system of one species will recognize and respond to antigens that are specific to that species, but may not respond to antigens from other species.