The immune response is mediated by a vast number of genes that govern both the rapid, nonspecific innate immunity and the slower, highly specific adaptive immunity. These genes control everything from pathogen recognition to immune cell development and signaling.
Key Genes in Innate Immunity
Innate immune response genes are typically "hard-wired" in the genome and encode for molecules that recognize molecular patterns common to pathogens.
Pattern Recognition Receptors (PRRs): These receptors recognize structures called pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs).
Toll-like Receptors (TLRs): Genes like TLR2, TLR4, and TLR9 recognize bacterial components, viral components, and more, initiating signaling cascades.
NOD-like Receptors (NLRs): Genes like NOD1 and NOD2 detect intracellular microbial components.
Signaling/Effector Molecules: Genes involved in the downstream inflammatory and antiviral response.
Cytokines and Chemokines: Genes such as TNF (Tumor Necrosis Factor), IL-1 (Interleukin-1), and Interferon (IFN) genes are critical for inflammation and coordinating the immune response.
Complement System Components: Genes encoding the plasma proteins that form the complement cascade (e.g., C1, C3, Factor B).
Key Genes in Adaptive Immunity
Adaptive immune genes are characterized by mechanisms that generate immense diversity, allowing for the recognition of virtually any antigen.
Antigen Receptor Genes: The defining feature of adaptive immunity is the creation of unique receptors on T and B cells.
Immunoglobulin (Ig) Genes (B cells): The genes for the heavy and light chains of antibodies/B cell receptors undergo V(D)J recombination (a unique somatic gene rearrangement) to create millions of different specificities.
T Cell Receptor (TCR) Genes (T cells): Similar to Ig, TCR genes also undergo V(D)J recombination to produce highly diverse T cell receptors.
Antigen Presentation Genes: These genes encode molecules that display antigens to T cells.
Major Histocompatibility Complex (MHC) Genes (HLA in humans): These genes encode the MHC Class I and MHC Class II proteins, which are crucial for presenting antigens to CD8+ and CD4+ T cells, respectively.
T Cell Activation/Differentiation Genes: Genes that control the activation and fate of T lymphocytes.
Cytokine Receptors and Transcription Factors: Genes for molecules like CD4, CD8, and master transcription factors such as T-bet (for Th1 cells) and GATA-3 (for Th2 cells) determine the specific adaptive response.
The Interplay of Innate and Adaptive Immunity
While distinct, the innate and adaptive systems are highly integrated. Many genes, particularly those encoding cytokines and chemokines, are expressed by cells of both systems and mediate their crosstalk. For example, dendritic cells (innate immunity) use their PRR genes to recognize a pathogen, process the antigen, and then use their MHC and costimulatory molecule genes to activate T cells (adaptive immunity), effectively bridging the two arms.