Internal Defense Mechanisms

Internal defense mechanisms emphatically constitute the ‘second-line of defense’ comprising
of the body’s internal mechanisms that may be critically mobilized against the highly specific invading
Mechanisms : The internal defense mechanisms are of two different types, such as :
(a) Non specific in action – e.g., phagocytosis, and
(b) Specifically aimed at the pathogens – e.g., sensitized cells, and antibodies.
Importantly, the above two different types are usually designated as nonspecific defense mechanisms
and specific acquired immunity*.
However, it is pertinent to state here that while the infection is active the two aforesaid mechanisms
virtually exert their action simultaneously in order to rid the body of the so called ‘invading
microbes’. In fact, this very interrelationship, and the interrelationships prevailing between the defense
mechanisms may be explicitely depicted

Nonspecific Defense Mechanisms
Mother nature has enabled the ‘human body’ so splendidly as to critically mobilize several
factors that act nonspecifically against the possible wide spread invasion by the ‘foreign organisms’.
Interestingly, such cardinal and vital factors essentially consist of the following four typical examples,
namely :
􀁑 complement system,
􀁑 phagocytosis,

􀁑 naturally occurring cytotoxic lymphocytes, and
􀁑 in terferon.
Each of the aforesaid factors shall now be treated individually in the sections that follows :
 Complement System
Higher animal’s serum usually made up of a particular group of ‘eleven proteins’, which are
highly specific in nature, and are widely referred to collectively as the so called complement system by
virtue of the fact that its action complements predominantly to that of some prominent antibody-mediated
reactions. In other words, the complement system critically enacts a pivotal role with respect to
the overall generalized resistance against the infection caused by the ‘pathogens’ ; and, therefore,
accounts for as the ‘principal mediator’ of the ensuing specific inflammatory response.
Mode of Action (Modus Operandi) : The various steps involved are as follows :
(1) When the very ‘First Protein’, belonging to cluster of elevan proteins, gets duly activated
there exist distinctly a prominent ‘sequential cascade’ whereby the ‘active molecules’ duly
come into being via the inactive precursors*.
(2) Some of the protein variants do get activated very much along the ‘sequential cascade’ that
may function as mediators of a specific response, and eventually serves as activators of the
next step.

Complement Fixation (or Attachment) : In a broader perspective, the complement system is
quite capable of attacking and killing the invading cells exclusively after the antibody gets bound to the

in cell attack. Summararily, it represents as the classical or antibody-dependent pathway that prevalently
need to be activated by specific antibody : C1, C4, C2 and C3.