Receptor Diversity
Unlike germline DNA, this type of genetic change occurs only in lymphocytes and is not inherited.
What is somatic recombination?
This type of B cell is activated for the first time upon encountering its cognate antigen.
What are naïve B cells?
These T cells recognize antigen presented on MHC class I molecules.
What are CD8+ cytotoxic T cells?
These immune cells only recognize antigens when they are presented as peptide fragments bound to MHC molecules.
What are T cells?
A loss of this T cell population or its function leads to widespread lymphoproliferation and multi-organ autoimmunity due to failure of peripheral immune restraint.
What are regulatory T cells (Tregs)?
This process randomly combines variable, diversity, and joining gene segments to generate diverse antigen receptors in developing lymphocytes.
What is V(D)J recombination?
This region of an antibody determines its isotype and effector function but not antigen specificity.
What is the constant (Fc) region?
This thymic process ensures T cells can recognize self-MHC molecules at low affinity.
What is positive selection?
A process where one helper T cell lineage limits another to prevent mixed or conflicting immune programs.
What is lineage cross-regulation?
In humans, both maternal and paternal alleles of HLA genes are expressed simultaneously, a pattern known as this.
What is codominant expression?
These enzymes introduce double-strand breaks at recombination signal sequences to initiate antigen receptor gene rearrangement.
What are RAG1 and RAG2?
This antibody class is best known for mediating allergic reactions and protection against parasitic worms by binding to mast cells and basophils.
What is IgE?
This T helper subset activates macrophages and is important for intracellular pathogens like viruses and some bacteria.
What are Th1 cells?
T follicular helper cells provide critical help to B cells during affinity maturation through cytokines and this receptor-ligand interaction.
What is CD40-CD40L? (costimulation)
This type of rejection typically occurs days to weeks after transplantation and is primarily mediated by T cells recognizing donor antigens.
What is acute rejection?
This enzyme is essential for both class switching and somatic hypermutation.
What is AID (activation-induced cytidine deaminase)?
This process allows a B cell to change the antibody isotype it produces without altering antigen specificity.
What is class switch recombination?
This T helper subset is critical for neutrophil recruitment and defense against extracellular bacteria and fungi.
What are Th17 cells?
Unlike autocrine cytokines that reinforce activation of the same cell, these cytokines shape lineage commitment during the earliest stages of T cell activation.
What are polarizing cytokines?
This transplant complication is essentially the immunologic “reverse” of rejection, where the immune system originates from the graft rather than the host.
What is graft-versus-host disease (GVHD)?
Autoreactive B cells in the bone marrow may be rescued from negative selection by this process, which involves continued immunoglobulin light chain rearrangement.
What is receptor editing?
This B cell subset provides a fast but relatively low-affinity antibody response to T-independent antigens, bridging innate-like and adaptive immunity.
What are marginal zone B cells?
In this model, interruption of TCR signaling after initial positive selection drives differentiation into this T cell lineage.
What are CD8⁺ T cells?
This cytokine acts as a key checkpoint determining which transitional B cells survive into the mature naïve pool.
What is BAFF?
In this pathway of graft rejection, donor proteins are processed by recipient antigen-presenting cells and presented as peptides on self MHC.
What is indirect allorecognition?