Innate Immune Responses and Host Defense

The immune system is comprised of two types of responses: innate (non-specific) and adaptive (specific). Innate immunity is present by default and is activated immediately following infection.

Non-specific immunity is so named because the protective response is the same regardless of the source of the infection. The adaptive immune system, in contrast hand, is slower, responds more specifically, and creates immunological memory.

Inflammation is the primary component of innate immunity. In order to limit the spread of infection and promote wound healing, injured cells produce cytokines and other pro-inflammatory substances (such as bradykinin, histamine, leukotrienes, prostaglandins, and serotonin). These pro-inflammatory mediators dilate blood vessels and attract phagocytes.

Neutrophils subsequently enhance the immune response by attracting leukocytes and lymphocytes. The Complement cascade is activated, which improves the innate response. Opsonization is a significant consequence of complement cascade activation. Pathogenic antigen opsonization marks invasive bacteria for ingestion and destruction by phagocytes.

The innate response includes a variety of cell types, but it is particularly reliant on basophils and mast cells (inflammation) as well as neutrophils and macrophages (phagocytosis). The innate immune system also stimulates the adaptive immune response by antigen presentation, which is an essential role.

Key points:

• Acute phase proteins
• Allergy, asthma and inflammation
• Co-stimulatory and co-inhibitory molecules
• Complement and coagulation
• Dendritic cells
• Granulocytes
• Innate lymphoid cells (ILCs)
• Interferons
• Lysosomal enzymes
• Monocytes/macrophages
• Pattern recognition receptors

The first line of protection against invading viruses is the innate immune response. They must also initiate certain adaptive immune responses. Innate immune responses rely on the body's ability to recognise pathogen conserved features that are not present in the uninfected host. Many types of molecules on microbial surfaces, as well as certain viruses' double-stranded RNA, fall within this category.
Toll-like receptor proteins, which are present in plants, invertebrates, and vertebrates, recognise many of these pathogen-specific compounds. Microbial surface molecules also activate complement, a group of blood proteins that work together to break microorganism membrane, target microorganisms for phagocytosis by macrophages and neutrophils, and create an inflammatory response in vertebrates.