An introduction to immunology and immunopathology

Fig. 2  Adaptive immunity: T-cell and B-cell activation and function. APC antigen-presenting cell, TCR  T-cell receptor, MHC major 

histocompatibility complex (figure adapted from images available at: 

http://en.wikip edia.org/wiki/Image :B_cell_activ ation .png

 and 

http://commo 

ns.wikim edia.org/wiki/Image :Antig en_prese ntati on.svg

)

---

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Marshall et al. Allergy Asthma Clin Immunol 2018, 14(Suppl 2):49

the production of cytokines of the IL-17 family, and 

are associated with ongoing inflammatory responses, 

particularly in chronic infection and disease. Like 

cytotoxic T cells, most Th cells will die upon resolution 

of infection, with a few remaining as Th memory cells 

[

2

, 

3

].

A subset of the CD4+ T cell, known as the regulatory 

T cell (T reg), also plays a role in the immune response. 

T reg cells limit and suppress immune responses and, 

thereby, may function to control aberrant responses 

to self-antigens and the development of autoimmune 

disease. T reg cells may also help in the resolution of 

normal immune responses, as pathogens or antigens 

are eliminated. These cells also play a critical role in the 

development of “immune tolerance” to certain foreign 

antigens, such as those found in food.

B cells

B cells arise from hematopoietic stem cells in the bone 

marrow and, following maturation, leave the marrow 

expressing a unique antigen-binding receptor on their 

membrane. Unlike T cells, B cells can recognize antigens 

directly, without the need for APCs, through unique 

antibodies expressed on their cell surface. The principal 

function of B cells is the production of antibodies 

against foreign antigens which requires their further 

differentiation [

2

, 

3

]. Under certain circumstances, B cells 

can also act as APCs.

When activated by foreign antigens to which they have 

an appropriate antigen specific receptor, B cells undergo 

proliferation and differentiate into antibody-secreting 

plasma cells or memory B cells (see Fig. 

2

). Memory 

B cells are “long-lived” survivors of past infection and 

continue to express antigen-binding receptors. These 

cells can be called upon to respond quickly by producing 

antibodies and eliminating an antigen upon re-exposure. 

Plasma cells, on the other hand, are relatively short-lived 

cells that often undergo apoptosis when the inciting 

agent that induced the immune response is eliminated. 

However, these cells produce large amounts of antibody 

that enter the circulation and tissues providing effective 

protection against pathogens.

Given their function in antibody production, B cells 

play a major role in the humoral or antibody-mediated 

immune response (as opposed to the cell-mediated 

immune response, which is governed primarily by T 

cells) [

2

, 

3

].