The interaction of innate immune and adaptive immune system

Abstract

The innate immune system serves as the body's first line of defense, utilizing pattern recognition receptors like Toll-like receptors to detect pathogens and initiate rapid response mechanisms. Following this initial response, adaptive immunity provides highly specific and sustained killing of pathogens via B cells, T cells, and antibodies. Traditionally, it has been assumed that innate immunity activates adaptive immunity; however, recent studies have revealed more complex interactions. This review provides a detailed dissection of the composition and function of the innate and adaptive immune systems, emphasizing their synergistic roles in physiological and pathological contexts, providing new insights into the link between these two forms of immunity. Precise regulation of both immune systems at the same time is more beneficial in the fight against immune-related diseases, for example, the cGAS-STING pathway has been found to play an important role in infections and cancers. In addition, this paper summarizes the challenges and future directions in the field of immunity, including the latest single-cell sequencing technologies, CAR-T cell therapy, and immune checkpoint inhibitors. By summarizing these developments, this review aims to enhance our understanding of the complexity interactions between innate and adaptive immunity and provides new perspectives in understanding the immune system.

Keywords: adaptive immunity; disease pathogenesis; immunotherapy; innate immunity.

FIGURE 1

Illustration of T cell activation by APC (using CD4 T cells as an example). The TCR recognizes and binds to the pMHC complex presented by the APC. The coreceptor CD4 binds to the MHC class II molecule, generating the first signal, which induces T cell activation. Additionally, the binding of CD80 and CD86 on the APC surface to CD28 on the T cell surface provides the second signal, also known as the costimulatory signal, which further induces T cell activation and proliferation. Cytokines secreted by the APC provide the third signal to the T cells, promoting the activation, proliferation, and differentiation of T cells.

FIGURE 2

cGAS–STING pathway. The figure shows the whole process from the recognition of the infection by cGAS to the production of the effect. First, cGAS senses DNA and forms cGAS–DNA droplets. ATP and GTP in this complex are catalyzed to produce 2′3′‐cGAMP.It binds STING and initiates the transport of STING from the ER to the Golgi. During translocation, STING recruits TBK1 and IRF3.Phosphorylation of STING by TBK1 leads to phosphorylation of IRF3 and translocation to the nucleus. This is followed by transcription of IFN‐I and many other inflammatory cytokines. Created with BioRender.com.

FIGURE 3

The cancer‐immunity cycle and TME. The figure shows the components of cancer immunity. The upper part shows the core of cancer immunity, a cyclical process of accumulation of immunostimulatory factors and amplification of the killing effect. This cycle can be simplified into seven steps, starting with the release of antigens from the death of cancer cells and ending with the killing of cancer cells by T cells. The other components of the TME are shown below. The TLS has an inner zone of CD20+ B cells surrounded by T cells, similar to the structure of lymphoid follicles in secondary lymphoid organs. Created with BioRender.com.