granulocytes White blood cells with multilobed nuclei and cytoplasmic granules. They comprise the neutrophils, eosinophils, and basophils. Also known as polymorphonuclear leukocytes.
granuloma A site of chronic inﬂammation usually triggered by persistent infectious agents such as mycobacteria or by a nondegradable foreign body. Granulomas have a central area of macrophages, often fused into multinucleate giant cells, surrounded by T lymphocytes.
Grass A serine protease of Drosophila that functions downstream of peptidoglycan-recognition proteins (PGRPs) and Gram-negative binding proteins (GNBPs) to initiate the proteolytic cascade leading to Toll activation.
Graves’ disease An autoimmune disease in which antibodies against the thyroid-stimulating hormone receptor cause overproduction of thyroid hormone and thus hyperthyroidism.
Griscelli syndrome An inherited immunodeficiency disease that affects the pathway for secretion of lysosomes. It is caused by mutations in a small GTPase Rab27a, which controls the movement of vesicles within cells.
group 1 ILCs (ILC1s) The subtype of innate lymphoid cells (ILCs) characterized by IFN-γ production.
GTPase-activating proteins (GAP)   Regulatory proteins that accelerate the intrinsic GTPase activity of G proteins and thus facilitate the conversion of G proteins from the active (GTP-bound) state to the inactive (GDP-bound) state.
guanine nucleotide exchange factors (GEFs) Proteins that can remove the bound GDP from G proteins, thus allowing GTP to bind and activate the G protein.
gut-associated lymphoid tissues (GALT)   Lymphoid tissues associated with the gastrointestinal tract, comprising Peyer’s patches, the appendix, and isolated lymphoid follicles found in the intestinal wall, where adaptive immune responses are initiated, and by lymphatics to mesenteric lymph nodes.
GVHD See graft-versus-host disease.
H-2 locus, H-2 genes The major histocompatibility complex of the mouse. Haplotypes are designated by a lower-case superscript, as in H-2b.
H-2DM See HLA-DM.
H-2O See HLA-DO.
H2-M3 A nonclassical MHC class Ib protein in mice that can bind and present peptides having an N-formylated amino terminus for recognition by CD8 T cells.
H5N1 avian flu A highly pathogenic inﬂuenza subtype responsible for ‘bird ﬂu’.
haploinsufficient Describes the situation in which the presence of only one normal allele of a gene is not sufficient for normal function.
hapten carrier effect Antibody production against a small chemical group, the hapten, following its attachment to a carrier protein for which an immune response has been generated.
haptens Any small molecule that can be recognized by a specific antibody but cannot by itself elicit an immune response. A hapten must be chemically linked to a protein molecule to elicit antibody and T-cell responses.
Hashimoto’s thyroiditis An autoimmune disease characterized by persistent high levels of antibody against thyroid-specific antigens. These antibodies recruit NK cells to the thyroid, leading to damage and inﬂammation.
heavy chain, H chain One of the two types of protein chain in an immunoglobulin molecule, the other being called the light chain. There are several different classes, or isotypes, of heavy chain (α,δ, ε, γ, and μ), each of which confers a distinctive functional activity on the antibody molecule. Each immunoglobulin molecule contains two identical heavy chains.
heavy-chain-only IgGs (hcIgGs) Antibodies produced by some camelid species composed of heavy-chain dimers without an associated light chain that retain antigen binding capacity.