Page 797 - Veterinary Immunology, 10th Edition

VetBooks.ir Adjuvants

To maximize the effectiveness of vaccines, especially those
containing killed organisms or highly purified antigens, it has been

common practice to add substances called adjuvants to the vaccine
(adjuvare is the Latin verb for “to help”). Adjuvants can increase the
speed or the magnitude of the body's response to vaccines, they
may permit reductions in the amount of antigen injected or the
numbers of doses administered, they can induce appropriate bias in

the response (Th1 or Th2), they may trigger cell-mediated
immunity, and they are essential if long-term memory is to be
established to soluble antigens. Adjuvant use is critical for the

effectiveness of subunit or recombinant vaccines. The “science” of
adjuvants has historically been empirical. In other words, materials
were added to vaccines to see if they improved either the strength
or duration of the immune response. As a result, adjuvants
appeared to be randomly selected substances and their mechanisms

of action were speculative. Recently, however, it has become clear
that the commonly employed adjuvants are toll-like receptor
ligands. Their main mode of action is to promote antigen uptake,

processing, and presentation by dendritic cells. In general,
adjuvants trigger innate immune responses that in turn act on
dendritic cells to enhance antigen presentation to T or B cells (Table
24.3). As our knowledge of the ways in which dendritic cells and T
or B cells interact has grown, it has become possible to develop

vaccines designed rationally to maximize antigen presentation.
Thus the growing use of particles coated with antigen, cytokines,
and co-stimulatory molecules as adjuvants has led to encouraging

improvements in vaccine efficacy.

TABLE 24.3

Some Common Adjuvants

Type Adjuvant Mode of Action
Depot adjuvants Aluminum phosphate Slow-release antigen depot?
Aluminum hydroxide Slow-release antigen depot?
Alum Activate DAMPs
Freund's incomplete adjuvant Slow antigen release depot
Microbial adjuvants Anaerobic corynebacteria Macrophage stimulator

797