Yes, there are cases in which IgG antibodies can cause the agglutination of red blood cells (RBCs). Research has shown that agglutination of RBCs by IgG antibodies depends on the density of antigen sites at the RBC surface, suggesting that agglutination by IgG antibodies might be due to specific cross-linking. Additionally, a study on the anti-IgG-induced agglutination of RBCs using a sensitive, automated antiglobulin test demonstrated that normal RBCs agglutinated strongly with anti-IgG antibody, indicating the presence of IgG on the erythrocyte membrane. Therefore, while IgM antibodies are known for directly agglutinating RBCs, IgG antibodies can also cause agglutination through specific cross-linking.
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