VDJ rearrangement occurs so that: Select one: a.after a pathogen has entered the system, B cells can then construct receptors that will bind to that specific pathogen  (custom-made BCR) b.there can be millions of different BCR on B cells already present when a pathogen enters the system, some of which are likely to bind that pathogen  (make lots of BCRs and hope some of them work) c. the combinations of V, D and J segments create BCRs specific for all the pathogens that humans have evolved with (similar to PRR, but a wider range of target molecules)

Wiskott–Aldrich syndrome is an immunodeficiency disease due to mutations in the gene encoding WASp. Individuals with this disease make poor antibody responses to protein antigens, due to impaired T cell help for B cells. WASp-deficient T cells are likely impaired in providing adequate help to B cells due to: A. Defects in up-regulating expression of genes encoding cytokines required by B cells B. Defects in up-regulating metabolic pathways for T cell macromolecular synthesis C. Defects in up-regulating expression of genes needed for T cell survival D. Defects in cytoskeletal reorganization needed for directed T cell cytokine secretion E. Defects in up-regulating T cell integrin adhesion for stable interactions with B cells

Toll-like receptors represent an ancient pathogen-recognition system. The first pattern recognition receptor (PRR) important in innate immune responses was discovered in the fruit fly Drosophila melanogaster. Stimulation of this receptor, called Toll, induces: The synthesis of prostaglandins and leukotrienes The inflammatory response in Drosophila hemolymph vessels The production of antimicrobial peptides The recruitment of phagocytic cells to the site of infection The activation of Drosophila complement

Virus infections induce production of interferons that act on infected cells to enhance their recognition by CD8 cytotoxic T cells. To counter these mechanisms, viruses often encode proteins that interfere with antigen processing and presentation. In an experiment, cells infected with Virus X are treated with interferon and compared with uninfected cells treated with interferon. Proteasomes are isolated from the two cell populations and their enzymatic activities are compared. The data in figure below show the amino acid preferences for cleavage of peptides by the two samples of proteasomes. Based on these data, Virus X most likely encodes a protein that interferes with: The expression of MHC class I on the surface of the infected cell The rate at which peptides are produced from intact proteins in the infected cell The transport of peptides from the cytosol to the endoplasmic reticulum in the infected cell The replacement of constitutive proteasome subunits with immunoproteasome…