Molecular immunity represent the 'second' arm of immunological reactions (the first being cellular immunity). It must be remembered that this distinction is arbitrary, as there is a close interaction between the cells and molecules involved in host defense. Immune response molecules are involved in the recognition of pathogens, the activation of the immune system and also in effector systems that eliminate the infecting pathogens. Some of these molecules are found on the surfaces of immune cells, or may be secreted into the extracellular fluid. Others are located within cells (e.g. cytoplasmic vesicles). In the following pages, we will examine the key features of some of these immune response molecules.

Proteins that recognise and bind to non-self are receptor proteins. The receptors of the adaptive immune system of the vertebrates are called antigen receptors (e.g. antibodies, T-Cell Receptors and the Major Histocompatibility Complex). The receptors of the innate immune system are called Pattern Recognition Receptors (PRRs), as they recognise "microbial molecular patterns" (an example of a PRR is the Toll-like Receptors). Indeed, the microbial molecules recognised by the PRRs are called Pathogen Associated Molecular Patterns (PAMPs) or Microbe Associated Molecular Patterns (MAMPs).

Sham Nair 2014