Complex sentence: Some studies have shown it to be available for HIV infection on the surface of the cell clustered around the CD4 protein yet conflicting studies have shown that it is not available on the cell surface but instead is found in significant amounts in the blood plasma.
Split into simpler sentences: Some studies have shown it to be available for HIV infection on the surface of the cell clustered around the CD4 protein. Yet conflicting studies have shown that it is not available on the cell surface, but instead is found in significant amounts in the blood plasma.