The change in morphology and behavior of a mature or immature B cell during an immune response, resulting from exposure to a mitogen, cytokine, chemokine, cellular ligand, or an antigen for which it is specific.

The attachment of one cell to another cell via adhesion molecules, where both cells are part of the same organism.

The invasion by an organism of a cell of its host organism. The host is defined as the larger of the organisms involved in a symbiotic interaction.

The attachment of a cell, either to another cell or to an underlying substrate such as the extracellular matrix, via cell adhesion molecules.

Penetration by an organism into the body, tissues, or cells of the host organism. The host is defined as the larger of the organisms involved in a symbiotic interaction.

A small, elongated secretory organelle that forms part of the apical complex, located along the main axis of an apicomplexan parasite cell within the extreme apical region and at the periphery under the inner membrane complex. Of the specialized secretory compartments identified in apicomplexans, micronemes discharge their contents first, during initial contact of the parasite's apical pole with the host cell surface. Micronemal proteins function during parasite attachment and penetration into the target cell.

All of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures.

A lipid bilayer along with all the proteins and protein complexes embedded in it an attached to it.

The volume enclosed by the microneme membrane.