*2.2.1. B lymphocytes*

elimination of tumor cells as well as in response to injury and trauma. Thus, an effective and efficient immune system is essential as a host defense mechanism against infectious diseases and cancer. The immune system can be further subdivided into innate and acquired or

**Physico-chemical barriers** Skin Cutaneous and mucosal immune systems

Monocytes/macrophages T lymphocytes

Innate immunity is the first line of defense mechanism against the invading agents present at birth. The innate immune system includes physico-chemical barriers, circulating molecules, immune cells as well as soluble mediators [1, 2]. As compared to acquired immunity, innate immunity has no memory, poor specificity and has immediate response with lower potency.

The acquired or adaptive immune response is the second line of defense mechanism which offer better protection against re-exposure to the same pathogen [2]. The acquired immune system is further subclassified into humoral mediated immunity which involves antibody production by B lymphocytes and cell mediated immunity comprising CD4+ and CD8+T lymphocytes. Acquired immunity has immunological memory and it is highly specific. The specificity occurs because each lymphocyte carries surface receptors for a single antigen [1]. When compared to innate immunity, it has slower response, however it is much more potent

Innate and adaptive immune systems as well as complement counteract each other to produce

Lysozyme Stomach acid

106 Trends in Basic and Therapeutic Options in HIV Infection - Towards a Functional Cure

Commensal bacteria in gut

**Circulating molecules** Complement Antibodies

**Immune Cells** Granulocytes B lymphocytes

Natural killer cells

**Table 1.** Components of the innate and acquired immune systems [1].

and robust and the response varies among individuals.

an effective function and mechanism of eliminating the invading agents.

**Soluble mediators** Macrophage-derived cytokines Lymphocyte-derived cytokines

**Innate immunity Acquired immunity**

Mucosal membranes Antibodies in mucosal secretions

adaptive immunity (Table 1).

**2.1. Innate immunity**

**2.2. Acquired immunity**

B lymphocytes are known by their ability to produce antibodies (immunoglobulins), which are specific for particular antigen [1]. Antibodies work in several ways to combat invading pathogens. Some pathogens, particularly viruses and some bacteria as well, infect individuals by entering cells. Some of these pathogens escape humoral immunity and later on will be encountered by cell-mediated immunity, which is conferred by T lymphocytes.
