Human Leukocyte Antigen and Platelet Immunology
Human Leukocyte Antigen HLA antigens and antibodies are also
involved in transfusion and transplantation medicine Responsible
for reactions that causes chills and fever in red cell transfusion
The genes are part of Major Histocompatibility Complex (MHC)
located in Chromosome no. 6 2nd to ABO compatibility in organ
transplant, important in the survival of kidney, heart and lung
transplants Essential in recognition of self and non-self, and
coordination of cellular and humoral immunity, and the immune
response to antigens Naming of HLA antigens consist of letter
designating the locus: A, B, C, DR, DQ, DP, and a number of
indicating A2, B27, CW7, DR1, DQ5Testing and Identification of
Antibodies Identified by agglutination or hemagglutination test
Class I- found in surface of platelets, leukocytes and most
nucleated cells (Mature red cells lack HLA Ag) Class II - found in
antigen presenting cells - macrophages, dendritic cells, and
B-cells; not found in plateletsSerologic Typing Suspension of B or
T lymphocytes is added to microtiter plates containing known
antibody specificities. After incubation, a rabbit complement is
added If the Ab on the plate matches the Ag on the cell, complement
is activated causing cell injury or a positive reaction
Cell damage is detected by the addition of a dye - injury allows
the dye to enter the cell and visual means to see (+) cells Each
well is seen under the microscope and identified whether Class I or
IISensitization of HLA Ag Pregnancies: about 30-50& of women
with 3 or more pregnancies develop HLA antibodies Blood
transfusion: about 50% of patients who receive multiple
transfusions develop AB. Thus, leukocyte reduced blood may decrease
sensitization. Previous transplant: about 90% of patients develop
HLA antibodies within 2 weeks of failed graft Therefore,
cross-matching with the recipient serum with T cells and B cells
from the potential donor is important to avoid rejection and
Graft-versus-host disease (GVHD). GVHD - occurs when a grafter
immunocompetent cells from a donor mount an immune response against
a host tissue. Symptoms: diarrhea, rash and jaundice. Can also
occur in immunocompromised patients receiving blood components from
related donor. Thus, irradiation of blood components from first
degree relative is performed to reduce the risk of leukocytes
proliferation in the host4. Irradiation - reduce viable leukocytes
from replicating
Platelet Antigens Platelets possess inherited membrane; can
elicit an immune response Platelet Abs are less frequently found
because of less Ag variability in the population Abs to platelets
Ags are the major cause of: . Neonatal Alloimune Thrombocytopenia
(NAIT) - inherited from the father; cause platelet reaction. Post
Transfusion Purpura (PTP) - characterized by antibody destruction
of platelets after transfusion
