A Focused Review of Basic Immunology Concepts

Abstract Fundamentally, red blood cells (RBC) transfusion constitutes the most commonly performed organ transplant in all of medicine. Numerous immunologic considerations must be undertaken when transfusing RBCs and platelets to patients to prevent alloimmunization, and ensure not only the feasibility of future transfusions, but also ensuring fetal safety of future pregnancies, and even that of potential hematopoietic stem cell or solid organ transplants. Because the concepts of antigen recognition, processing and presentation by the innate immune system to cells of the adaptive immune system, and subsequent humoral immune responses underlie the basis of RBC alloantibody formation, it is important to begin with a very generalized review of these foundational immunology concepts. This way, the reader has a basis with which to understand discussions later in the text regarding platelet refractoriness, transfusion support during hematopoietic stem cell transplants, and RBC alloimmunization in general. This chapter is meant to serve as a refresher for those with basic immunology education, and in no way represents a comprehensive review of these topics. We will provide a very brief discussion of antigen recognition by innate immune cells, antigen processing, and presentation via major histocompatibility complex molecules to cells of the adaptive immune system. We will also discuss the unique nature of B-cell and T-cell receptor formation, and how they contribute to antigen recognition diversity. We will then discuss activation of the adaptive immune system, the concept of immunologic self-tolerance, and focus on different types of humoral responses and the concept of humoral immunologic memory. We will then briefly introduce the complement cascade focusing on its function in RBC hemolysis. Throughout, we will maintain a generalized conceptual approach due to space constraints, and will focus on applying these concepts to transfusion medicine.