Basic Pathological Mechanisms March 17-19 Flashcards
Which isotype of antibody has two heavy chains, two light chains, four distinct subclasses and crosses the placenta to provide fetal protection?
IgG
Thymus dependent humoral responses are typically associated with which type of molecules?
Proteins
Which marker best defines a cell as a cytotoxic T lymphocyte?
CD8
Viral transformation reduces the MHC molecules on epithelial cells. Which cells are most likely to respond to destroy the infected cells?
Natural killer cells
What is a characteristic structural motif of an antibody molecule?
beta-pleated sheet
Positive and negative selection of T lymphocytes occurs where?
thymus
What is the precursor cell that matures into a mature CD4+ T cell?
an alpha/beta or gamma/delta T cell
What are properties of IgA?
has J chain; has a secretory piece important for transport; the PIG receptor for this molecule is on the basal surface of epithelial cells; has the highest rate of synthesis of all major isotypes
What is the importance of CD28?
T cell activation to produce effector and memory cells
What are properties of adaptive immunity?
clonal distribution of receptors, enhance by prior exposure, immunological memory, vast range of molecular discrimination, and takes a few days to weeks to develop response
Who discovered antibodies?
German physiologist Emil von Behring
Describe innate immunity.
limited range of molecular discrimination; non-clonal distribution of receptors; not enhanced by prior exposure; relatively rapid response (hours)
What is difference between humoral and cell-mediated immunity?
humoral: antibodies
cell-mediated: effector molecules bearing specificity for antigen (TCR)
What are the functions of B cells?
synthesis and secretion of antibodies;
immunological memory;
homing to specific anatomic locations;
presentation of antigens to T cells (co-stimulation of T cells);
cytokine secretion (T cell activation and lymphoid organogenesis)
Describe B cell affinity maturation.
selection within germinal centers (access to follicular B helper T cells)
Describe thymus-dependent humoral responses.
antigens are proteins; class II MHC molecules on B cells present peptide to CD4+ helper T cells; B cells receive help from CD4+ T cells (CD40L on T cell, cytokines released from T cell)
Describe thymus independent humoral responses.
type 1: non-protein with ability to bind TLRs or other innate immune receptors
type 2: antigen with repeating structure (pneumoccocal capsular polysaccharide)
Which humoral response is activate in the absence of all T cells?
TI-1 antigen (polyclonal B-cell activation; repeating epitopes)
What happens when B cells are activated?
antibody secretion by plasma cells; neutralization (prevents bacterial adherence), opsonization, and activation of complement
Describe humoral response to conjugate vaccine.
B cell binds bacterial polysaccharide epitode linked to tetanus toxoid protein; antigen is internalized and processed; presented to T cell; production of antibodies
What interleukin is important in the collaboration of B and T cells?
IL-4
Describe germinal centers.
in secondary lymphoid tissues, such as spleen, lymph node, and Peyer’s patches
composed of B lymphocytes, follicular dendritic cells, and follicular helper T cells
increased expression of Bcl-6; follicular helper cells secrete IL-21
site of class switch recombination, somatic hypermutation, and affinty-based selection responsible for affinity maturation
generates memory B cells and long-lived plasma cells
Describe memory B cells.
are generated from both TD and TI responses
In TD responses, can be generated through germinal center dependent and independent pathways (associated with isotype switching and hypermutation)
TI responses typically have not undergone isotype switching or somatic hypermutation
length of antigen exposure may influence the relative proportions of different types of memory B cells
Describe long-lived plasma cells.
generated in germinal centers
reside in bone marrow
persistence depends on expression of Mcl1 (less antibody diversity compared to memory B cells)