Types of Immunity

 Immunity:

Resistance offered by host against the micro organisms/Foreign substance

Types:

1.Innate immunity:

    Present right from birth;

    Respond to microbial antigens shared by multiple microbes

    Components:

        1.Anatomical barriers

        2.Physiological barriers

        3.Phagocytes

        4.NK cells

        5.Mast cells

        6.Dendritic cells

        7.Complement pathway (Alternate pathway and Mannose Pathway)

        8.Fever and inflammatory response

        9.Cytokines-TNF,Interleukins(IL 1,IL 6,IL 8,IL 12,IL 16,IL 18),IFN alpha,beta,TGF beta

        10.Acute phase reactant proteins

2.Adaptive/Acquired immunity: Resistance against infecting foreign substance that an individual acquires /adapts during his life

    Types:

       (i) Active:

            Produced actively by host immune respone

            Infection(Natural)

            Vaccination(Artificial)

            Long Lasting

            Lag phase present

            Memory present

            Negative phase may occur

Active immunity is of 2 types

   (a) Primary:

        Immune response against primary antigenic challenge 

        Slow, sluggish (appear late) and short lived 

        Lag period is longer (4–7 days) 

        No negative phase 

        Antibody produced in low titer and is of IgM type.

        Antibody producing cells: Naive B cells 

        Both T dependent and T independent antigens are processed.

     (b)Secondary:

         Immune response against subsequent antigenic challenge

         Prompt, powerful and prolonged (long lasting)

        Lag period is absent or short (1–3 days)

         Negative phase may occur

        Antibody produced in high titer and is of IgG type

         Antibody producing cells: Memory B cells

        Only T dependent antigens are processed

(ii)Passive immunity:

    Received passively

    Mother to fetus(Natural)

    Ready made antibody transfer(Artificial)

    Short term

    No lag phase

    Immunologic memory not present

Other types:

Local (or mucosal) Immunity

    Local or mucosal immunity is the immune response that is active at the mucosal surfaces

such as intestinal or respiratory or genitourinary mucosa:

• It is usually mediated by a type of IgA antibody called secretory IgA.

• Local immunity can only be induced by natural infection or by live vaccination, e.g. after

OPV (but not by killed vaccines).

Herd Immunity

Overall immunity of a community (or herd) towards a pathogen:

Herd immunity plays a vital role in preventing epidemic diseases. 

If the herd immunity is good, that means large population of the community are immune towards a pathogen.

Hence, epidemics are less likely to occur and eradication of the disease may be possible.

• Elements that contribute to create a strong herd immunity are:

○○ Occurrence of clinical and subclinical cases in the herd

○○ Ongoing immunisation programme

○○ Herd structure, i.e. type of population involved

○○ Type of pathogen: Herd immunity may not be strong in a community against all

the pathogens.

• Herd immunity develops following effective vaccination against some diseases 

Adoptive Immunity

It is the process of transfer of CMI from one individual to other.

• It occurs following injection of immunologically competent T-lymphocytes known as

"Transfer factor".

• It is useful for treatment when the CMI is low, e.g. in lepromatous leprosy