self-interest threat

First consider if the audit client is a bank: "A firm, an audit team member, or any of that individual’s immediate family shall not accept a loan, or a guarantee of a loan, from an audit client that is a bank or a similar institution unless the loan or guarantee is made under normal lending procedures, terms and conditions." "materiality" doesn't come into this - the transaction must be on NORMAL lending terms. For a non-bank client, "lending" is not its business and as you say, is only permitted if it is immaterial to the client AND the recipient (firm/audit team member/immediate family member). This does not require safeguards - if immaterial to the client it can have no bearing on the financial statements.