[1] He has made pioneering contributions to immunology and was the first to discover marginal zone B-cells.
[2] He was elected a Fellow of the Royal Society (FRS) in 2012, his nomination reads:Ian MacLennan has made several landmark contributions to immunology and especially our understanding of antibody production.
His classic experiments led him propose a role for germinal centres in affinity maturation of antibody responses by a process of hypermutation followed by antigen-mediated selection.
Subsequently, he identified the basis of the multi-step selection process that protects against autoantibody production.
He also first discovered marginal zone B cells and identified how they counter encapsulated bacterial infection.