Antibody response to technetium-99m-labeled sheep erythrocytes in mice treated with anti-lymphocyte serum and concanavalin A

In the present series of experiments we have studied the effects of anti-lymphocyte serum (ALS) and concanavlin A (Con A) on the immune response to technetium-99m-labeled sheep erythrocytes (SRBC) and have related this to the localization and persistence of antigen at the site of induction and antibody synthesis. The number of ^99mTc-labeled SRBC in the spleen and liver was quantified by gamma scintillation counting and the cellular kinetics of the splenic antibody response was determined by means of the hemolytic plaque technique. After injection of normal rabbit serum (NRS)-treated control mice with 4 × 10^{8 99m}Tc-labeled SRBC, the number of cells localizing in the spleen ranged from a high of 4.2 × 10⁶ on Day 1 to a low of 1.7 × 10⁶ on Day 4, while the number in the liver ranged from a high of 68.8 × 10⁸ on Day 1 to 18.6 × 10⁶ on Day 4. The number of splenic plaque-forming cells (PFC) increased from 321-429 on Day 1 to 93,000-101,000 PFC on Day 4 and this was paralled by a rise in serum hemagglutinin and hemolysin titers. In mice treated with ALS on the other hand, splenic localization initially was increased 10-fold, hepatic localization was unchanged, and the antibody response was markedly suppressed. Splenic PFC ranged from approximately 100 between days 1 and 3 and increased to only 500 on Day 4. Mice which received Con A on Day - 1 had a reduction in splenic PFC which ranged from 150 on Day 1 to 1900 on Day 4. Splenic localization of ^99mTc-labeled RBC initially was three- to fourfold greater than that in NRS-treated mice and then decreased to control levels. The increased numbers of SRBC detected in the spleens of immunosuppressed mice at the time of peak response can be attributed to decreased in vivo lysis by reduced numbers of splenic antibody-producing cells.