Introduction

The adaptive immune response is a critical aspect of the vertebrate immune system, responsible for providing long-term immunity against pathogens and tumors. This response is characterized by the specific recognition and destruction of antigens, achieved through the activation of lymphocytes – T cells and B cells. The adaptive immune response offers a high degree of flexibility and versatility, as it can generate an effective response against a diverse array of pathogens, and can also provide immunological memory to facilitate rapid and targeted responses in future encounters with the same antigen.

In this comprehensive course, we will delve into the intricacies of the adaptive immune response, exploring its key components, mechanisms, and regulatory processes. We will examine the role of T cells and B cells, as well as their receptors, activation, differentiation, and effector functions. Furthermore, we will investigate the fundamental concepts of antigen presentation, immune tolerance, and immunological memory.

T Cells

T cells, or T lymphocytes, are a critical component of the adaptive immune response. They originate from hematopoietic stem cells in the bone marrow and migrate to the thymus for maturation into mature T cells.

T Cell Receptors (TCRs)

T cells express a unique receptor known as the T cell receptor (TCR), which is composed of two chains: an alpha chain and a beta chain, or a gamma and a delta chain in certain cases. The TCR recognizes specific antigenic peptides presented on the surface of antigen-presenting cells by Major Histocompatibility Complex (MHC) molecules.

Activation, Differentiation, and Effector Functions

Activated T cells differentiate into effector T cells, which can be further classified into helper T cells and cytotoxic T cells. Helper T cells aid in the activation and differentiation of B cells, as well as the recruitment of other immune cells to the site of infection or damage. Cytotoxic T cells directly attack and destroy infected cells by releasing cytotoxic granules that contain enzymes such as perforin and granzymes.

B Cells

B cells, or B lymphocytes, are another essential part of the adaptive immune response. They originate from hematopoietic stem cells in the bone marrow and mature in the bone marrow and spleen.

B Cell Receptors (BCRs)

B cells express a receptor called the B cell receptor (BCR), which is composed of an antigen-specific antibody molecule and an associated immunoglobulin complex. The BCR recognizes specific antigens on the surface of pathogens or antigen-presenting cells.

Activation, Differentiation, and Effector Functions

Activated B cells undergo clonal expansion to produce large numbers of plasma cells that secrete antibodies – proteins designed to bind specifically to the original antigen. These antibodies serve various functions, such as neutralizing pathogens, tagging them for phagocytosis, and aiding in complement activation.

Antigen Presentation

Antigens are foreign molecules that trigger an immune response. Antigen presentation is the process by which antigens are presented to T cells in a way that they can recognize them as harmful. This process involves two types of antigen-presenting cells: dendritic cells and B cells.

Major Histocompatibility Complex (MHC)

The Major Histocompatibility Complex (MHC) is a set of genes that encode proteins involved in antigen presentation. MHC molecules present peptides derived from intracellular pathogens or antigens to CD4+ helper T cells, while another class of MHC molecules, called Class I MHC, presents peptides to CD8+ cytotoxic T cells.

Immune Tolerance

Immune tolerance refers to the mechanisms by which the immune system is prevented from attacking self-antigens and maintaining self-tolerance. There are several types of immune tolerance, including central tolerance (occurs in the thymus and bone marrow) and peripheral tolerance (occurs outside the thymus and bone marrow).

Immunological Memory

Immunological memory is the ability of the adaptive immune system to remember previous encounters with specific pathogens or antigens, allowing for a rapid and targeted response upon re-exposure. This is achieved through the activation and maintenance of memory T cells and B cells that can quickly respond to reinfection by recalling their original specificity.