Use of LOR-15C9 monoclonal anti-D to differentiate erythrocytes with the partial D^VI antigen from those with other partial D antigens or weak D antigens

Historically, red blood cells (RBCs) with partial D antigens have been defined serologically by their pattern of reactivity with polyclonal and monoclonal anti-D. Although numerous variants have been described in tests with well-characterized monoclonal anti-D, definition remains difficult to ascertain serologically. RBCs of known partial D type were tested with LOR-15C9 (a monoclonal anti-D) and commercial anti-D by the tube indirect antiglobulin test (IAT), by micro typing system IgG gel cards, and by immunoblotting. By IAT, LOR-15C9 reacted strongly with D^IIIa, D^IIIc, D^Va, D^VI, D^VII, and DFR RBCs in addition to RBCs with common D antigens; weakly with D^II, DNU, and D^IIIb RBCs; and not at all with D^IVa, D^IVb, DBT, or R₀^Har RBCs. Reactivity was variable (1+ to 4+), with RBCs classified as weak D (D^u). As expected, the commercial anti-D agglutinated all D variants and weak D RBC samples by the IAT and by using IgG gel cards; however, the reactivity with D^VI RBCs was weaker than with LOR- 15C9. By immunoblotting, LOR-15C9 detected a band with an apparent molecular mass of approximate M^r 30,000-34,000 in membranes prepared from D-positive, D^IIIa, D^IIIc, D^Va, D^VI, D^VII, and DFR RBCs and an additional band of Mr 20,000-22,000 in membranes prepared from D^VI RBCs. No band(s) was detected in membranes from D^II, DNU, D^IIIb, D^IVa, D^IVb, DBT, R₀^Har, weak D, or D-negative samples. LOR-15C9 provides a useful tool to identify positively D^VI samples and thereby differentiate this partial D from other D variants and from weak D samples.