Human Immunity and Blood

Cytokines are a broad category of small proteins that are important in cell signalling. Their release has an effect on the behaviour of cells around them. Proinflammatory cytokines are produced predominantly by activated macrophages and are involved in the up-regulation of inflammatory reactions. There is abundant evidence that certain pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α are involved in the process of pathological pain.

Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. They are essential for fighting infections and for subsequent immunity. Phagocytes provide the second line of defence which is considered as a non-specific defence because it destroys invaders in a generalized way without targeting specific pathogens. Phagocytes are activated when the pathogen is able to cross the first line of defence.

Neutrophils are the most abundant type of granulocytes. They form an essential part of the innate immune system. Neutrophils undergo a process called chemotaxis via amoeboid movement, which allows them to migrate toward sites of infection or inflammation. Neutrophils express and release cytokines, which in turn amplify inflammatory reactions by allowing other neutrophils, monocytes, eosinophils attachment to endothelium and dilation of capillaries is seen to increase the blood flow to the affected area.

Chemical barriers protect against infection. The skin and respiratory tract secrete antimicrobial peptides such as the β-defensins. Enzymes such as lysozyme and phospholipase A2 in saliva, tears, and breast milk are antibacterial substances. Vaginal secretions serve as a chemical barrier following menarche, when they become slightly acidic, while semen contains defensins and zinc to kill pathogens. In the stomach, gastric acid serves as a powerful chemical defence against ingested pathogens.

Innate immunity refers to nonspecific defence mechanisms that come into play immediately or within hours of an antigen's appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells such as neutrophils that attack foreign cells in the body.  Polymorphonuclear leukocytes (PMNL - neutrophils) are the granulocytes characterized by the presence of granules in their cytoplasm. They provide innate immunity.

The second line of defence involves non-specific cellular and molecular responses of the innate immune system because these defences do not differentiate between different types of the pathogen and respond the same way upon every infection. Mucous membrane, phagocytes and lysozyme are all involved in a non-specific defence mechanism, whereas, killer T-cells or cytotoxic T-cells provide the third line of defence.

• Cytokine inhibits viral replication.
• They form an innate immune system by forming physical barriers. 
•  Virus-infected cells secrete proteins called interferons which protect non-infected cells from a further viral infection is a cytokine barrier. Hence, The cytokine barrier among these is interferon.

As the altitude increases, the atmospheric pressure decreases. Thus reducing the level of oxygen. People living at higher altitudes are used to the lower density of oxygen molecules in the air. They have higher levels of haemoglobin (red blood cells) in their blood which helps them to take in more oxygen. In contrast, people living at lower altitudes have lesser haemoglobin concentrations as they experience a higher density of oxygen molecules in the air.

Kupffer cells are specialized macrophages located in the liver that play a key role in the immune system by phagocytosing pathogens and debris.

Phagocytes have the ability to phagocytose or kill foreign cells and particles like pathogens by ingesting them. Many blood cells have this function, including monocytes, neutrophils and macrophages. Basophils do not have phagocytic activity.

Thus, the correct answer is 'Basophil.'

Among the White blood cells (WBCs) four cells have the phagocytic ability. The neutrophils, monocytes, eosionophils and basophils. The basophils and the eosinophils have very less phagocytic ability when compared to the phagocytic ability of neutrophils and monocytes. When monocytes leave the blood and enter tissue spaces they grow and modify to form macrophages which still have the phagocytic ability. Thus, the correct option is B.

A macrophage is a type of phagocyte, which is a cell responsible for detecting, engulfing and destroying pathogens and apoptotic cells. Macrophages are produced through the differentiation of monocytes, which turn into macrophages when they leave the blood. Macrophages also play a role in alerting the immune system to the presence of invaders. Phagocytosis is the term used to describe the engulfing and destroying of defective or microbial cells. When inflammation occurs, monocytes undergo a series of changes to become macrophages and target cells that need eliminating. Once engulfed, cellular enzymes inside the macrophage destroy the ingested particle. Some macrophages act as scavengers, removing dead or necrotic cells while others provide host immunity by engulfing microbes.

An antibody also known as an immunoglobulin (Ig) is a large, Y-shaped protein molecule produced by B lymphocytes, that is used by the immune system to identify and neutralize pathogens (antigens) such as bacteria and viruses.