Question

Explain the infected a mucosal surface by bacterial pathogen. ( immunological responses)

Answer 1

Mucosal surfaces are composed of epithelial cells and these cells form a barrier between hostile external environments and the internal milieu. Mucosal surfaces have selective permeability barrier and are responsible for nutrient absorption and waste secretion.The mucosal surfaces of the body are particularly vulnerable to infection. They are thin and permeable barriers to the interior of the body because of their physiological activities in gas exchange (the lungs), food absorption (the gut), sensory activities (eyes, nose, mouth, and throat), and reproduction (uterus and vagina). The necessity for permeability of the surface lining these sites creates obvious vulnerability to infection and it is not surprising that the vast majority of infectious agents invade the human body through these routes.

THE MUCOSAL IMMUNE RESPONSE AGAINST BACTERIAL PATHOGEN.

Mucosal tissues are major barriers to the entry of pathogens into the body. The IgA (and sometimes IgM) antibodies in mucus and other secretions can bind to the pathogen, and in the cases of many viruses and bacteria, neutralize them. Neutralization is the process of coating a pathogen with antibodies, making it physically impossible for the pathogen to bind to receptors. Neutralization, which occurs in the blood, lymph, and other body fluids and secretions, protects the body constantly. Neutralizing antibodies are the basis for the disease protection offered by vaccines. Vaccinations for diseases that commonly enter the body via mucous membranes, such as influenza, are usually formulated to enhance IgA production.

Immune responses in some mucosal tissues such as the Peyer’s patches in the small intestine take up particulate antigens by specialized cells known as microfold or M cells (Figure ). These cells allow the body to sample potential pathogens from the intestinal lumen. Dendritic cells then take the antigen to the regional lymph nodes, where an immune response is mounted.

IgA Immunity. The nasal-associated lymphoid tissue and Peyer’s patches of the small intestine generate IgA immunity. Both use M cells to transport antigen inside the body so that immune responses can be mounted.

The immune system can be divided into a series of functional anatomical compartments, of which the two most important are the peripheral lymphoid system made up of the conventionally studied spleen and lymph nodes, and the mucosal lymphoid system. Specific homing mechanisms for lymphocytes to each of these compartments serve to maintain a separate population of lymphocytes in each. The mucosal surfaces of the body are highly vulnerable to infection and possess a complex array of innate and adaptive mechanisms of immunity. The adaptive immune system of the mucosa-associated lymphoid tissues differs from that of the rest of the peripheral lymphoid system in several respects. The types and distribution of T cells differ, with significantly greater numbers of γ:δ T cells in the gut mucosa compared with peripheral lymph nodes and blood. The major antibody type secreted across the epithelial cells lining mucosal surfaces is secretory polymeric IgA. The mucosal lymphoid system is exposed to a vast array of foreign antigens from foods, from the commensal bacteria of the gut, and from pathogenic microorganisms and parasites. No immune response can normally be detected to food antigens. Indeed, soluble antigens taken by mouth may induce antigen-specific tolerance or antigen-specific suppression. In contrast, pathogenic microorganisms induce strong protective TH1 responses. It is an important challenge to understand these contrasting specific immune responses. The key distinction between tolerance and the development of powerful protective adaptive immune responses is the context in which peptide antigen is presented to T lymphocytes in the mucosal immune system. In the absence of inflammation, presentation of peptide to T cells by MHC molecules on antigen-presenting cells occurs in the absence of co-stimulation. By contrast, pathogenic microorganisms induce inflammatory responses in the tissues, which stimulate the maturation and expression of co-stimulatory molecules on antigen- presenting cells. This form of antigen presentation to T cells favors development of a protective TH1 response.