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Chapter 9 : Memory and Infection
Category: Immunology; Clinical Microbiology
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This chapter reviews the basic principles of adaptive immunological memory. It first discusses the dynamics of T-cell responses, and commitment to memory lineage. Large numbers of memory T cells were located within nonlymphoid tissues. The chapter then focuses on maintenance and longevity of memory T cells. Development of antigen-specific antibody responses can be either T-cell-independent or T-cell-dependent. The majority of vaccines and viral infections trigger high affinity, antigen-specific B-cell responses that are CD4 T-cell-dependent. The differential migration of memory B cells (MBCs) and plasma cells (PCs)/plasmablasts is most likely accomplished by changes in the expression pattern of different chemokine receptors and other adhesion molecules. Induction of a durable neutralizing antibody response represents the basis of many successful vaccines and is important to the maintenance of protective immunity against a wide range of pathogens. Analysis of humoral immunity against tetanus and diphtheria toxins revealed that not all antibody responses last a lifetime. Humoral immunity is maintained by two types of B cells—MBCs and PCs. The duration of the PC response is most commonly measured indirectly by quantitation of antigen-specific serum antibody levels or directly through the use of the ELISPOT assay. Finally, the chapter focuses on models explaining long-lived humoral immunity. Antibody responses to antigens result in slowly declining antibody responses that last for decades, whereas immunity against viral infections such as measles, mumps, and rubella will often last a lifetime.
Dynamics of primary versus secondary T-cell response. Primary T-cell responses are slow to develop, result in the selective expansion of pathogen specific clones, and establish a long-lived increase in the frequency of pathogen specific T cells (memory). Secondary (recall) responses are faster, larger, and more efficacious, and induce a long-lived boost in the number of memory T cells.
Duration of serological memory is dictated largely by the antigen under study. In this illustration (adapted from Amanna et al., 2007 ), the durability of antigen-specific antibody responses following infection or vaccination are compared over time. Antibody responses to EBV, measles, mumps, rubella, and vaccinia last a lifetime with little to no decrease in titer. Antibody responses to VZV decline more rapidly than antibody responses to other viral infections but remain more durable than the antibody responses to protein antigens such as tetanus or diphtheria. In general, the durability of serum antibody responses differ greatly depending on the antigen under study, and if the underlying mechanisms involved with determining the persistence of antibody can be elucidated, this will have important implications in terms of optimizing future vaccine design.
T-cell properties vary with differentiation state and anatomic location a
Duration of serum antibody production after infection or vaccination a