The innate immune system in Mycobacterium infection.
The innate immune system provides an early response against invading microorganisms while the adaptive immune system operates at later stages when the pathogen has infected the host. In the first hours of exposure to and invasion by the pathogen, two outcomes can be schematically described: rejection/destruction of the pathogen (by innate immunity) and infection of the host (despite innate immunity).
 

Immunological memory and the germinal centre reaction

The immune system requires the cognate interactions of T cells, B cells, and antigen presenting cells to respond to invading antigens/pathogens. The peripheral organs where the immune response occurs are organized into microanatomic compartments that are composed of T cell zones and B cell follicles. B cell responses to thymus dependent (TD) antigens begin in the T cell zones of secondary lymphoid tissues where T and B cells initiate antigen and costimulus dependent proliferation. These initial cognate interactions are essential for humoral immunity, but alone result in only transient, low affinity antibody responses. It is a subsequent set of cellular encounters, collectively known as the germinal centre (GC) reaction, that drives affinity maturation and memory.