Cellular Events in Type IV Hypersensitivity (Delayed)

Esch esch at aol.com
Tue Feb 7 23:53:29 EST 1995


The classic tuberculin DTH reaction appears after injection PPD into
individuals previously exposed to Mycobacterium tuberculosis.  24 hours
after injection the site in inffiltrated by mononuclear cells (50%
lymphocytes, 50% monocytes, in man polymorphs are not present).  By 48
hours, mostly lymphocytes are present and they distrupt the dermis and
collect around blood vessels, secreting lymphokines.  Fibrin deposits
form, trapping more lymphocytes and "debris".  This mass is the induration
that has become the hallmark of the skin reaction.  Since many of us have
not been exposed to M. tuberculosis, the Candida albicans DTH reaction
(more complex because CBH, Ab-mediated components are present) is
preferred to test an intact cell mediated immune response.



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