Immunology began as the study of how bacteria and viruses were taken care of by the individual. In the beginning at the beginning of the 20th century it was very much an antibody affair but in the 1970s it became an intensely cellular story with its own hormone system so called interleukins.
It turns out that microorganism are neutralized by cells, so called phagocytes that ingest and degrade material. Antibodies are formed and can neutralize by themselves but also opsonize, ie, adhere to cells and make targets more tasty. There is also cellular toxicity of various kinds. Blood serum contains so called complement that can punch holes in bacteria.
The interesting problem in immunology is how we recognize specifically the target for neutralization. How can we recognize foreign from self? It so happens that we construct during our development a repertoire of molecules that can recognize targets by tolerizing the self molecules. The spleen and lymphnodes are involved in this.
Antibodies are Y-shaped proteins that are produced by a special type of white blood cells. In the two tips of the Y one finds so called hypervariable regions, ie, in these tips the amino acid sequence can vary a lot and thus it can form many different surfaces that can bind to the target. There is a special area in the genome of an individual that generates this variability.
Emil von Behring (1854-1917) described antibody activity against diphtheria toxin for the first time in 1890. Paul Erlich (1854-1915) laid down his side chain theory in 1900. He concluded that toxins must have chemical structures just like the dyes he worked with, the side chains of which gave rise to different colors. Recognition in the immune system must depend on shapes. In 1904 Almroth Wright (1861-1947) described opsonization by phagocytes.
In the 1920s, Michael Heidelberger (1888-1991) and Oswald Avery (1877-1955) described antigen (target) antibody complex formation and also showed that antibodies were made of protein. Then in the 1940s Linus Pauling confirmed the lock-and-key model of antigen-antibody binding. The Clonal Selection Theory came in 1957 by Frank Macfarlane Burnet (1899-1985). The theory explains how tolerance is created by selecting negative for self antigen. Lymphocytes with the specificity for self antigens are killed during development.
Data from Wikipedia