(5) Recent published data indicate that C4 is also fragmented in a similar
fashion, possibly by the same inactivator. Thus, RBCs sensitized "in vivo" with C4 have
only C4d present on their surface.
(6) Generally, the commercial houses standardize their antiglobulin serums
against RBCs sensitized with C3, C4, and C3d. The cells are usually sensitized with
complement by complement-binding blood group antibodies (for example, anti-Lewis or
anti-I) and/or low ionic strength methods. The C3d-sensitized cells can be from patients
with autoimmune hemolytic anemia or cells prepared "in vitro", by treating C3b-
sensitized red blood celIs with C3 inactivator (for example, in normal serum) or trypsin.
1-21. POLYSPECIFIC ANTIGLOBULIN REAGENTS
a. Polyspecific antiglobulin reagents are used for routine compatibility tests,
alloantibody detection, and the DAT. They contain antibody to human IgG and to the
C3d component of human complement. Other anticomplement antibodies may be
present, including anti-C3d, anti-C4b, and anti-C4d.
b. Since most clinically significant antibodies are lgG, the most important
function of polyspecific antiglobulin is to detect the presence of IgG.
1-22. MONOSPECIFIC ANTIGLOBULIN SERUMS
a. As discussed previously, the antiglobulin serum, used routinely in the blood
bank for procedures such as compatibility testing, usually reacts with several plasma
proteins (particularly IgG and complement). It is possible to prepare monospecific
antiglobulin serums by injecting animals with highly purified proteins, such as lgG, IgA,
lgM, C3, or C4; or by absorbing unwanted antibodies from the antiglobulin serum, the
first method being preferable (See Table 1-2).
b. The main use of monospecific antiglobulin serums is to extend the direct
antiglobulin test by evaluating which protein is responsible for the positive direct
antiglobulin test obtained with the broad-spectrum reagent (see Lesson 2, Section I).
On occasion, monospecific reagents such as anti-lgG and anti-C3 may be of value in
the indirect antiglobulin test to show different patterns of reactivity when mixtures of lgG
noncomplement-binding and complement-binding antibodies are present
(for example, anti-hr" (e) + -Leb). The technique used for testing RBCs with these
reagents is exactly the same as that for broad-spectrum reagents.
Never use anti-IgA, -lgM, -C3, -C4 alone for compatibility testing or for